I am a big supporter of consolidated skill groups as I have been using them for many years, and the players of all my groups have greatly liked their uses.
One aspect I brought in was the concept of "trained ability checks" into my skill groups.
In example: Sometimes a straight up Strength check is required, but often similar feats of strength are needed where it would be reasonable to assume that someone who has trained (taken skill points) in strength related skills, might be better at the task than someone who has not taken any training. This same logic can be applied to all of the character's abilities.
Accordingly I have been using the following skill categories:
Athletics (Comprised of Climb and Jump), STR based
a good catch all category for anything involving a feat of strength check on any similarly trained areas.
Nimbleness (Comprised of Balance, Tumble & Escape Artist), DEX based
a good catch all category for anything involving an agility check on any similarly trained areas, yet not warranting a reflex saving throw.
Hardiness (Comprised of Concentraion), CON based
a good catch all category for anything involving an endurance related check on any similarly trained areas.
Note: I really do hope that they break this apart again from Spellcraft.
Analysis (Comprised of Appraise and Dechiper), INT based
a good catch all category for anything involving an intellectual reasoning check on any similarly trained areas.
Note: I really hope they break speaking a language apart from Decipher. Speaking extra languages is a great benefit, and one that should come from a specific skill cost to do so. If they want to simplify things, then I wouldn't object to just combining speaking with read and write for each language learned.
Intuition (Comprised of Sense Motive), WIS based
a good catch all category for anything involving an intuitive related check on any similarly trained areas. I also deem this skill to give general "streetwise" knowledge.
Note: I have also played around at including spot and listen into this, but I dedcided that they were not "intuitive" enough to include in this category. Instead I combined them into a skill called "Awareness" -- although Pathfinder has done the same and called it "Perception".
Diplomacy (Comprised of Diplomacy and Gather Information), CHA based
a good catch all category for anything involving a personal interaction / social grace related check on any similarly trained areas.
Because of the combined skill groups, I usually decrease the number of skills some classes get if a lot of their usual skills are included in the skill groups.
I can see where you are going, but for few skills missing, it's just like making ability checks!
Essentially, yes. The problem with ability checks is that it is rare to have any bonuses / modifiers to these straight up checks. When player's are asked to make ability checks, they usually moan because they involve relying totally on a random die roll (and on average adding -1 to +3 on the result for their ability modifier).
Ability checks are a poor way to determine a character's success with any given task because of this. Skills and other related modifiers were introduced to help take some of the randomness out of a d20 roll. Now if ability checks were a d20 + ability modifier + BAB then at least it would be somewhat scaleable.
As a DM I have found that these proposed skill categories make it easier to quickly resolve situations that arise -- especially those involving overlap into one or more skill categories (i.e., a player is going to jump off a staircase, grasp onto a rope mid-leap, swing across an entryway, crash through a window and land feet-first on a wagon outside).
Although I do like the idea of synergies, I did find trying to play with them to be far too cumbersome as they tend to be situational bonuses. I noticed that players either forget about their situational synergy bonus, or just add their situation synergy bonus to all of the related skill checks, regardless of whether the situational bonus was triggered.
For the sake of simplification, if a skill warrants granting a flat skill bonus to another skill, then the skills should be combined -- which is what they have already done.