Yay, another place to talk about free to play models. Because I haven't done this before
Anyways, people wondering about extreme punishments for bans, it's a valve game, on steam, it will be VAC protected, which means that valve DO have the option of VAC banning the steam account which prevents the use of online games on that steam account, ANY GAME. IE, average people wont troll because it'll cost them the game library, wont stop dedicated trolls from making new accounts and so on but at least there's that punishment in place as possibility (though, I honestly doubt they'll use it considering what I see in League regarding 'OMG HE MADE MISTAKE REPORT HIM')
Unlocking characters slowly like any slow unlock content system is a good free to play model. I'd be willing to bet that valve would love to go with it to because it certainly brings in a good chunk of cash but there's two factors stopping it being likely:
1) DOTA1 exists, doesn't matter if people don't want to actually play it (like me, I don't like playing it) if they can point to it and go 'why am I unlocking/buying heroes if this exists' it'll undermine any attempts to charge for heroes.
2) it's a big thing up on League to allow anyone to have all the heroes, gives a big incentive for League players to switch over to DOTA2 or at least try it. If you don't think that Valve aren't eyeing up that tasty top of the genre money then your sorely mistaken.
Frankly I actually have to say this: I like having champions limited for lower skilled players, it encourages repeated playing, allowing players to get comftable with one hero and as a result start to learn aspects of the game as a whole rather than worrying about playing their character correctly.
And regarding people saying that competitive play would be undermined by this
Seriously, any 'competitive' player (or someone who at least thought of themselves as such) would likley by whatever packages (and I'll bet my left nut there WILL be launch packages if it's F2P) that contain game content and it'd become a non factor. Complaining that a game requires a money investment before you can compete is like saying you should be able to play competitive CS on a crappy internet connection, lovely in theory but not gonna happen.