Benefit to pursuing numerous skills?

I don't see anything that actually prevents people from maxing everything out, unless there's a skill/level cap that I'm unaware of...

I've levelled block (albeit slowly) wearing light armor, so it's not impossible, just not recommended I imagine.

So far I've seen no downside to levelling everything. You just get more exp. Given, that the exp you receive after levelling my 9th skill to 5 is 1 exp per level, it's still exp!
So in other words, you're better off smashing 4 of your proficiencies much higher than the others, to get the increased exp for higher proficiency milestones...

Example: I level two handed from 1 to 2, I get 50 exp. Sweet! I level two handed from 10 to 11, I get 100exp?! Awesome. Continue this trend and you'll get exp faster than people who level up every skill to 10, then every skill to 20, as the exp returns diminish.

EDIT: In regards to the block skill, examine your weapons and compare them to the shields available. Each item has a block value, and that's the bonus that you roll with (including the bonus from block abilities and such) to attempt to riposte. The fastest way to level block is actually hitting your ripostes, so I suggest taking the first block ability to riposte on every 5 points above as opposed to 10, to make the skill infinitely easier to level. Some weapons such as the Halberd, Spear, Quarterstaff, have quite high block values for 2handed weapons, (6 at level 1 I think), and are quite viable for a two handed block based character. Your ripostes will also do a load more damage, but you sacrifice the armor you gain and the ability to shield bash when wielding a shield. Shield bashing can be done during block without leaving the block stance, hence it's quite useful.

The trade off is time. The more skills you're leveling, the more you have to do those skills to level them. Which means you could be level 5 with 15 in X number of skills or be level 5 with 25 in x-3 skills.

Previously there was a cap of 25 Talents over the life of the character, pretty sure that's still in place. Even after you take all 25 of your talents, you can still level every skill to 100 if you really wanted to, it's just they won't get the benefit of any of those Talents.

Some of the higher level talents have really high requirements in terms of skill level, so you should keep that in mind,too. You can stockpile talent points indefinitely, it's not like D&D where you have to spend everything every time, so to get the really high level stuff you might have to hold off with some points until your skill catches up. It's all under your control.