You're trying to build a strategy to migrate from
All of the popular frameworks are immature. They'll be completely different in a couple of years, and if you're lucky -- I mean really lucky -- they'll incorporate some sort of backward compatibility to let you leverage your existing code base. I wouldn't count on that though.
Of course, all that being said, if your principle work product is billable hours, then by all means go with the latest and greatest framework. The customer gets some great whiz-bang that they can pay another chunk of big money to upgrade in a few years. I mean, have you tried to hire an entry-level ASP programmer lately?
"It's a dog-eat-dog world out there, and I'm wearing Milkbone underware." -- Norm, from _Cheers_