With a total number of 280+ perks out of a max of 50 allowed, that is highly unlikely to ever occur. Next to impossible in fact. There will always be something useful for the player to take, even if it wasn't quite what you had hoped for. Fallout 3 had far less perks, and there was always something I had unlocked previously that I could take.
Hear me out. The idea that some people are suggesting is that when you pick a perk, you are limited to only perks from skills which you raised to contribute to the level up.
It is very likely that perks will still have skill level requirements, or else it would be possible to get all perks for a skill even if you've only raised that skill 12 to 20 times. I'm guessing these requirements will use the same 0, 25, 50, 75, 100 system that Oblivion's skill perks used. Let's take destruction for example, because it's the skill whose perk tree that we've gotten the best look at:
http://cdnstatic.gamesas.com/akqacms/files/tes/screenshots/SkillsMenu_wLegal.jpg
From that it looks like there will be 12 destruction perks: one level 0 perk, four level 25 perks, three level 50 perks, three level 75 perks, and one level 100 mastery perk.
- When you get to character level 20, your destruction skill is 50, and you choose one of the three level 50 perks.
- At level 21, your destruction skill is 51, and you choose another level 50 destruction perk.
- At level 22, your destruction skill is 52, and you choose another level 50 destruction perk. You've now gotten all the 8 destruction perks available until your destruction skill is at 75.
Then (for whatever reason), you do nothing but destruction, raising it up until you level up, but not quite to 75. But since you've already gotten all the destruction perks available below destruction level 75, and since you didn't raise any other skill between level ups, you can't pick any perk.
Now why would someone do that? I remember several times in both Morrowind and Oblivion where I would have tons of ingredients, then just turn them into tons of potions, raising my alchemy skill 10+ times and getting a level up just from alchemy alone. You could say "just use a variety of skills and that won't be a problem," but I don't see Bethesda implementing a system where there's even the
potential that that could happen. I think it's far more likely that when you level up you can choose a perk from any of the 18 trees, but you can only get perks which you meet the skill requirement for (25, 50, 75, 100).
There is one other possibility: the 280+ number does not include multi-level perks, so the actual number of "perks" that you can choose for a skill is greater than 12 to 20. But I thought I read somewhere that 280 includes the multi-levels.