If you truly want to upstream changes to libraries then I don’t see why lgpl code isn’t a choice for you. Use it in your proprietary code if you want, no changes no foul. If you make changes you just need to upstream or make the source available.
> If you truly want to upstream changes to libraries then I don’t see why lgpl code isn’t a choice for you.
Read LGPL a little more carefully. LGPL requires you to use it in a particular manner that lets any user swap out your version for their version, which basically means you're only allowed to dynamically link it as a shared library. Even if you make no changes to the library!
> that lets any user swap out your version for their version, which basically means you're only allowed to dynamically link it as a shared library
I had thought that the dynamic linking requirement was the only option according to the licence, but apparently not. According to 6.a. of v2 and 4.d.0. of v3 of the LGPL, it would be enough to give the user access to the source/object code of the main application and the compilation scripts under non-open-source terms, so that they can recompile and statically link it against their own version of the library.
