One of my goals throughout is to eliminate - or at least reduce- what I perceive as a bloat that has affected the game over time. If you look at the AD+D 1E Deities and Demigods (which I foolishly e-bayed a few years ago during a purge that I'm beginning to regret...) you'll notice (if memory serves) that the gods aren't all that impressive. Even the most powerful deities are in the low 20s as far as levels go.
I remember absolutely loving the idea that heroes in the Dragonlance setting (which didn't do a lot for me otherwise, but which I remember mostly for this element) was that characters were limited to level 15 as a punishment for hubris. I love this, and the idea that the B/X books terminate at level 14 fits perfectly for me.
Discussions of characters from fiction (especially conversations about Lord of the Rings) tend to come back to the idea that many of the great heroes aren't all that impressive level wise. Aragorn might only be level 8 or so. Gandalf could be built as a level 5 magic user if you really pushed it.
The fact that the demi-humans have hard caps that are relatively low (halflings can only get to level 8?) seem especially harsh when humans can get to level 36. That poor halfling is going to spend some 20+ levels sitting around watching others advance while he sits mired in what is, by contrast, the starting gate.
If humans cap at 14, then a dwarf getting to 12 or elf getting to 10 doesn't seem quite so bad anymore. Sure, they can't go as far as a human can - but they can get pretty close.
It re-frames the whole psychology of level advancement. One of (what I see as) the big errors that 4E made (from what little I know of it) is looking at levels 1-10 as the 'starter' levels, where you don't really get going to until level 11. That's just crazy to me. You don't need to conflate the leveling process and speed up experience (as Tenkar discussed with his readers at some length) if the leveling process caps out in the low teens. What's the hurry?
My instinct now is to leave the core rules relatively neutral on the whole issue of level caps. Can you go past level 14? Maybe... the rules won't tell you one way or the other. However, the setting book will make it clear that 14 is the cap progression for mortals in the Splintered Realm. After that, you are entering the realm of immortals, and that's VERY hard to do...
Skills and Some Thoughts:
The other ancillary benefit to this is that it builds in a cap to progression of skills and abilities. Let's say (for instance) that your target for any 'skill check' is 20. At 20, you succeed. In most cases, you get to add your level and the ability modifier to your roll. As a level 3 magic user with Lore as a skill, you always roll d20 and add your INT modifier (let's say you have 18 INT, so +3) and your level (+3). d20 +6 to see if you find out this piece of lore, target 20. Odds are not good for you (you need a 14 or better), but then again, that's old school D+D, isn't it? You weren't guaranteed of much. If you're rolling, it's because it's difficult. Even if we say that all skills have a default bonus of +2, this increases your total modifier as a level 3 MU to +8, still giving you less than a 50% chance. Pushing this all the way to level 14, you now have +2 (base) +3 (INT) +14 (level) for a total modifier of +19. You only fail on a roll of 1 when checking for 'standard' lore (target 20) and even difficult lore (+4 to the target or target 24) would need a roll of 5 or better on the die. Then again, you are as smart and as experienced as you could possibly be.
I have to think more about this skill thing, but I like where it's headed...