Out of curiosity, how many skill points do the PCs have now??
Because to get to a pyramid of
xxxx
xxxx
xxxx
xxxx
xxxx
xxxxx
Which is the absolute max you can get to with a Skill cap of 6 (All 25 skills are used at that point)
You need a total of 85 skill points.
Are you really close to that ??
(that's about 150 to 200 sessions assuming a significant milestone every 3-4 sessions... respect)
Even more extreme:
If you keep increasing the cap, you'll eventually end up with a column 25 high and 1 wide, which would require 325 skill points to fill.
If you can keep your game running that long that is *g*
Plenty of room for advancement i think :-P