That post is very long and actually got a few things wrong so I'll try to portray the key points that aren't wrong here.
This is the relevant feat description
Savage Species, p. 30
WIS 13, ability to assume a new form magically,
You learn to use a single supernatural ability of another kind of creature while assuming its form through a polymorph self spell or a similar effect.
Races of Eberron p.110
When you use your minor change shape ability to assume the form of a humanoid creature, you can also emulate any of that humanoid's subtypes.
So the first point is that the Racial Emulation feat directly says Minor Change Shape lets you assume the form of other creatures magically. Therefore it not only satisfies the prerequisite of Assume Supernatural Ability, but it also lets you benefit from its effects.
But the people who oppose this say that there's an additional requirement for the feat to function. That you must not only assume the form of another creature, but you must also do it using a polymorph self spell or an effect that is specfically similar to polymorph self. Then they say Minor Change Shape is not a "similar effect" to polymorph self because it does not bestow ability score and natural armor changes and the like, it doesn't have the polymorph subschool, and it's similar to disguise self therefore can't be similar to polymorph self.
So here are the counter arguments to that claim.
Definition of Similar
having a likeness or resemblance, especially in a general way:
Counter Argument 1: They're all under the same section "Changing Forms" in Rules Compendium p.24-26. The Changing Forms section in Rules Compendium is divided into 3 sections: Changing Forms, Revised Spells, and Druid.
Changing Forms: Alternate Form and Change Shape
Revised Spells: Polymorph, Shapechange
Druid: A Thousand Masks (exact copy and paste of Minor Change Shape), Wild Shape
So the counter point here is, all of these abilities have the same effect called Changing Forms. So how can abilities that have the same effect and do the same thing not be called "similar"? Because one is located under Revised Spells and the other under Druid? Revised Spells are so different from Druid abilities that form changing abilities under those two subsections are not similar? That's nonsense imo.
Counter Argument 2: 3.0 Alter Self is directly said to be similar to Polymorph Self and Shapechange.
Savage Species p.159
Alternate Form (Su): At 2nd level a barghest can assume the form of a goblin or an unusually large wolf as a standard action. This is similar to using the polymorph self spell but allows only these two forms.
Savage Species p.192
Alternate Form (Su): A rakshasa can assume any humanoid form, or revert to its own form, as a standard action. This ability is similar to the alter self spell cast by an 18th-level sorcerer. A rakshasa can use this ability the indicated number of times per day at the indicated duration. Eventually the rakshasa can remain in an alternate form indefinitely
Savage Species p.100
Alternate Form: Shauganttha can assume the form of a Tiny to Large viper (see the Snake entry in the Monster Manual). This ability is similar to a shapechange spell cast by a 19thlevel sorcerer but allows only viper forms. He uses the viper’s poison since he has no poison attack of his own.
3.0 Alter Self
The character can alter the character's appearance and form-including clothing and equipment-to appear taller or shorter, thin, fat, or in between. The assumed form must be corporeal. The character's body can undergo a limited physical transmutation, including adding or subtracting one or two limbs, and the character's weight can be changed up to one-half. If the form selected has wings, The character can fly at a speed of 30 feet with poor maneuverability. If the form has gills, the character can breathe underwater.
The character's attack rolls, natural armor bonus, and saves do not change. The spell does not confer special abilities, attack forms, defenses, ability scores, or mannerisms of the chosen form. Once the new form is chosen, it remains for the duration of the spell. If the character is slain, the character automatically returns to the character's normal form.
If the character uses this spell to create a disguise, the character gets a +10 bonus on the character's Disguise check.
So Savage Species, the book that printed Assume Supernatural Ability, directly says Alternate Form is similar to Polymorph Self and Shapechange, and it also directly says 3.0 Alter self is similar to Alternate Form. So by basic logic, 3.0 Alter Self is similar to Polymorph Self and Shapechange.
So why is this important? First, it definitely dispels the notion that alternate form is not similar to polymorph self or shapechange just because it's not a spell. Therefore it dispels the notion that only things with the polymorph subschool can be deemed similar to polymorph self since Alternate Form, being not a spell, cannot have a subschool.
Second it also directly dispels the notion that in order for something to be similar to polymorph self it requires changes to natural weapons, ability score, natural armor, etc. because 3.0 Alter Self literally has none of that.
Counter Argument 3: They override each other. Simply put, you can't have both Alternate Form and Polymorph on at the same time. One effect makes the other irrelevant. How can abilities that do the same thing to the point they override each other not be "similar effects"?
Counter Argument 4: Both Player's Handbook and Rules Compendium directly say Disguise Self alters your form like Polymorph and Shapechange.
Rules Compendium p.67
Magic that alters your form, such as alter self, disguise self, polymorph, and shapechange
Player's Handbook p.73
Magic that alters your form, such as alter self, disguise self, polymorph, or shapechange, grants you a +10 bonus on Disguise checks
And don't forget, a Thousand Masks is like Disguise Self and it's located under the same section as Polymorph. This dispels the notion that something similar to Disguise Self cannot also be similar to Polymorph Self.
Counter Argument 5: Degree of similarity doesn't exist. There are people who say it's not "similar enough" to be a "similar effect". But that's completely wrong. The condition here is boolean. Can it be considered similar? y/n. And the answer is y for all the reasons stated above. Therefore the Minor Change Shape effect is a "similar effect" to Polymorph.
Counter Argument 6: The feat Assume Supernatural Ability doesn't require anything from the "similar effects" other than the ability to assume a new form magically. It doesn't ask for any natural armor, type changes, ability score changes, etc. So why would anything other than the ability to assume a new form magically be relevant?
In my opinion, any honest reading of the feat would say that Polymorph Self is just an example of an effect that lets you assume a new form magically and needing to be specifically similar to polymorph self is nonsense.
So given all of these facts and rule quotes, I can't help but think there is no gray area here. I can't help but think the rules say unambiguously that Minor Change Shape works with Assume Supernatural Ability 100% and it's dishonest to say otherwise. There is no room for other interpretations given how strong the above evidence is
But whenever the topic comes up be it on reddit or the giantitp, a ton of people absolutely vehemently denies it and the topic gets closed before a discussion can be had.
So... I was just wondering. Is there any legitimate reason that Assume Supernatural Ability doesn't work with Minor Change Shape? Did I miss something? Does Minor Change Shape work with Assume Supernatural Ability?