It is not open source software anymore, and your code is very unlikely to be often used (unless you build some way to sell it otherwise, and that requires a lot of time and money in marketing), see this. Probably, nobody will care about your framework. BTW, you are quite unlikely to get contributions if you are a commercial entity requiring a copyright assignment (notice that the FSF requires a copyright assignment, but it is non-profit, and that assignment is a big stopper to occasionally contribute to GNU projects).
I know an example (academically interesting) of such code: the CompCert project (a certified and proven C99 compiler). For academic (or personal) usage, the source code is freely available. But commercial licenses are available from AbsInt.
However, INRIA folks working on CompCert never claimed that it is open source software. AFAIK they don't want (or don't care about) external contributions (except perhaps by few selected academic partners).
For a framework or library, I would suggest to use the GPLv3 (not the LGPL) license. It is then restricting the free software to free software projects (since a GPLv3 library cannot be linked to a proprietary software without additional permission), but you won't own the improvements contributed by others.
You probably should hire a lawyer, and of course I am not a lawyer (and details depend upon the country, legal system, etc...)