I will keep this short, unlike most posts, I'll get strait to the point.
The permise about being able to change as you go is cool and all, but it ultimately breaks the game. You should be able to be a jack of all trades-master of jack sh*t but not master of everything! I also think it lowers the replayability because instead of starting again with a new character/race etc you can just change and instantly become a mage, assassin whatever.
Thats just my two cents, but from the lmited amount of posts I've read it seems people agree.
Should have left out the first line, then. And the last.

I thought the perks were tied to skills. Why would anyone change that. The idea with TES is to have options. Several classes in Oblivion had Marksman so why would you not tie the perks to marksman(kinda like they did)?
Oops! So much talk of classes has addled my thinking! Yes, perks are tied to skills, but my mind was going: "now, if there were classes, the classes would define what perks are available...". An easy mistake to make, considering perk trees now replaces classes. Faction-specific perks would still be tied to skills. It's just that you'd have different perks available depending on your faction.
No, most RPers have different characters that do different things. If they want to be an assassin they create that character. If the person gets the itch to play a different style character, they don't normally turn their assassin into a cleric. But then you get a FEW of them who will create a backstory where the character used to do one thing, but now does another. Which was still possible in Oblivion.
I'll also tackle this: That person who wants to RP a mage character has to use the lockpicking skill if they want to open the lock because that spell was removed from the alteration school. Should they use their imagination that the box is now open and they are looting imaginary treasure??
My mages don't open locks. Probably because I'm playing in character.