My earlier question led to a definitive RAW answer proving that Arms of the Astral Self can't be used for grappling, even if a feat like Tavern Brawler gave you a grapple check bonus action off of the unarmed strike provided by it.
However, I'm the DM at the table, and in my head this is absolutely a Rule of Cool situation; neither Tavern Brawler nor the Grappler feat is assessed as particularly potent in community sources such as RPGBot, thanks to the fact that requiring a hit to trigger a grapple adds an extra chance for failure to the grapple not normally present, and the freely available grapple+shove combo that can be achieved in a single action instead of two for the same pair of grapple checks provided in Grappler, the latter of which leaves you Restrained as a result. This is a subjective opinion, but for the sake of the game I'm running, I agree, and character in question took both feats with clear intentions for a specific type of kit to provide synergy with a core concept of the character.
I intend to alter the reach requirements to grapple on the bonus action grapple attempt provided by Tavern Brawler off of Arms of the Astral Self's unarmed attacks - reach for this grapple will be extended by 5 feet until broken, and the 'hands' of Astral Arms are likewise considered capable of establishing and maintaining a grapple (at regular reach, except when using Tavern Brawler's bonus action).
Grappler will work on any already-grappled target, including those grappled at 10 feet with Arms. All other grappling rules, including dragging a creature, shoving, escape rules, releasing, and effects that would move the target of the grapple outside that 10 foot range, will function normally.
What potential complications or disruptions with other rules might this alteration cause, if everyone at the table is good beforehand with understanding that this is a unique Rule of Cool, and not a precedent to start breaking other things?
I'm looking specifically at possible mechanics and situations that have no readily actionable RAW resolution as a result of this change being utilized in combat, so I can prepare for such potential surprises before such a scene happens and not bog down the experience with having to come up with a complicated arbitration on the spot.