A number of people have mentioned the trend towards multi-class PCs
I have recently been toying with the idea of restricting the maximum rank cap to 3+3/profession lvl for all favored categories (stacking where apropriate) and 3 +1/total lvlfor all other skills, the highest always applying. this would give a simple way to provide an advantage to characters who chooose to specialise, although a couple of other tweaks would be needed.
I share your annoyance with endless multi-classing, but i don't think this mod will help at all. I think that most people already tend not to buy too many ranks in out-of-favored-categories for the very reasons that they cost 4 per rank and those DPs would generally best be spent elsewhere. If a PC is happy to spend 4/rank and max out in the number of ranks (at 3 + 3/lvl) without multiclassing, that's fine by me. But your mod would, IMO, simply further encourage focused spending in class-favorited categories with the intention of switching classes when the majority of skill-bonus returns on DP expenditures became too measly to be concerned with in comparison to gaining proficiency in a whole new category of skills offered by a class-switch.
At that point, you switch quickly to another class with favorited-categories you want to develop next and max your development until the same critical mass is reached, drawing your eye to the
next class (and because some favorited-categories will overlap from multiclass to multiclass, you'll still be able to continue pumping DPs into a whole bunch of already highly-developed skills).
Spell spheres other than universal would count as thier own skill category.
Not sure what this means, precisely. How would it be implemented vis-a-vis casters, or is this just a shot at the Rogue?
Talents for arcane power etc would be removed, as would eloquence.
I hate these talents too. Eloquence is definitely a pet peeve: who wouldn't take it and why exactly shouldn't fighters have something similar apply to all their combat skills? Fighters shouldn't have anything like this, and neither should spell-users. Why didn't the HARP-masters just use it the same way RM did? Reduce all casting rounds by 1 to a minimum of 1? That essentially means that your spell-user can negate one -10 penalty to any spell if (s)he's speeding up the casting time. That means negating a single -10 versus the existing, constant(!), +25 to
all spell-casting.
Mage classes would gain a +10 to any professional spell/5 levels (7 levels for warrior mage)
If you got rid of Eloquence I'd say absolutely to this mod.