The Non-combat proficiency system isn't that bad. It just needs a couple tweaks and can easily pass as a 3rd style skill system....just add additional NCP points at creation, and maybe tweak the rate at which they're gained when leveling to whatever you feel sounds appropriate and add a few new proficiencies to cover things with no current skills, and allow retries on things that make sense to allow additional chances. Instead of a DC, you just make a bonus or penalty on the roll depending on how easy or hard the check is. Attempting a skill you aren't proficient in applies an +3 penalty on top of other modifiers, and an additional +3 penalty for attempting skills from pools you don't have normal access for (a fighter attempting an non-proficient wizard pool check would have +6 to the roll, but only +3 to a skill from the warrior or general pool, though a particularly intelligent fighter could still potentially have a chance at pulling it off. While a Bard would only get +6 attempting to use priest pool skills, since they get regular access to all pools but priest). The first point in a NCP spent removes the penalty, while each additional point gives a bonus to check results.
I'd also add new NCP that can replicate some thief skills in the rogue pool, but are less efficient, since they're taking up NCP points, and have high dex/int penalties (Thieves can simply ignore these and use their class based skills instead), and for non-bards would cost 2 NCP per point, unless a kit changed that access.