Your thoughts? I think it will be like this: Chris's scenario around 8 hours, Leon's one around 8 too and Alex's around 5 hours and of course don't forget rumored Ada's scenario I think hers will last for 4 - 5 hours.

Idk what to think really. A lot of developers really are getting lazy when it comes to campaigns. I remember when games used to take SO long to beat, but now you can get a game and beat it in a day or two with the exception of such games like Mass Effect, Fallout and Skyrim. But I really do hope Capcom can deliver nice lengthy campaign scenarios for each character, but right now I'm only expecting about 4 or 5 hours each.

Chris and Leon will be probably weigh in with about five/six hours each on first playthrough, then various extra scenarios adding about five hours?

Even if they WERE just 5 hours each, they're still bigger than most games nowadays. So I don't mind even if it IS just 5h / scenario. That isn't to say that I'd like it longer.

Scenario-wise that is.

My guess for a speed run leaderboard placing around 5-6hrs (maybe even a 3-4hr). Thus normal game time should be around the 9-12hr mark like in re5. Given that, maybe 3-4hrs per scenerio with the 3 main protagonist

Remember the older re series was always around the 9hr mark if you take your time to explore in the first playthrough or at least that's the time i took :P

Leon & Chris = 5-6 hours each
Baldy = 3-5 hours
Ada = 3-4 hours

That wouldn't be too bad 13 hours for the stories I care about most. Anything is better than MW2's 2 1/2 hours.

I don't expect the main campaign to last any longer than 13 hours, so divide that anyway you want. I expect the Wesker dudes campaign will be the shortest, Leon the longest. Bonuses should add a ton of replay value.

Dlc scenarios otw most likely?

If they are even near the quality of LIN and DE I would buy.
though a costume, character, or weapon should come with them for use in Mercs,Story,etc.

Most later Biohazard titles are 12-18 first run experiences, so like David said, divide that any way you'd like. If somehow this game were to be completely different and massive, I'd be a happy guy.