We are discussing very different things here....
A commom IDE: Yes, it is possible, and it wouldn't be that much heavier than the ones we already have.... The parser would have to be upgraded for sure, but then again, even in a Multi-Platform IDE, you only work on one code base at a time...
So the parser could still be platform specific, and called upon by the active platform IDE....
The same for the Compilation.... You can only compile 1 platform at a time....
Still, it would open the possibility to have a "Compile All" mechanism, that would compile all platforms, One at a time!
Yes, B4i is a paid IDE, but that is "just" an enable/disable option....
In my opinion, The thing that poses the most problem, is the visual designer and Custom Views (specially platform specific CVs)