So, how I think it will work out, and how I hope it will work out, is that we start with our 28 points distributed in SPECIAL, and each perk has a SPECIAL requirement corresponding to its position on the perk chart, as speculated http://tamrielvault.com/group/fallout-character-building/forum/topics/perks-chart-news?xg_source=activity and elsewhere. That means, ranked perks notwithstanding, we would "grow into" our SPECIAL distribution by level 28; the highest level we've seen in the demos so far was 48. I imagine we'll be able to raise our SPECIAL by spending a perk point (visually, I imagine we'd spend the perk point on the SPECIAL row of the perk chart, but whatever), which would naturally let us meet the requirements of more perks. In essence, any perks not within our initial SPECIAL distribution would effectively cost two levels to obtain.
They've got to decide at what level our characters are effectively "complete", and design the endgame around that. But rather than just put a level cap there, I'd rather that would just be the point where the leveling curve goes exponential and it takes a lot more XP for each level. If we level at a similar rate to Fallout 3 and New Vegas, that will be around level 30; which would fall neatly in line with our initial 28 points of SPECIAL. If we level at a rate closer to Skyrim, that would be closer to level 50; Bethesda does like giving us a good amount of levels. And I've already pointed out that we would need to reach level 112 to max out our SPECIAL and take the first rank of every perk, so either way that's still more than twice as high as where I'm speculating (word: speculating) the endgame will be designed around. Naturally, it would svck if we managed to get as far as level 100 as quickly as we could reach level 30 in Fallout 3, so I'm hoping it starts slowing down as early as level 28.
If my speculation is close, there's really nothing lost from letting us advance our level beyond where the endgame is. We have to prioritize a playstyle as we develop the character, and we'll be going through the vast majority of the game's content with that developing character, not a maxed out master. Hell, there's already somewhat of a predecent for this: Fallout 2 let us level up and take perks all the way to level 99, although the endgame was designed around level 24. In fairness, Fallout 2 didn't let us max out our SPECIAL, and we'd have to take the Mutate! perk to respec our traits.