(I work at RemObjects) - we've been working hard on reducing convergence recently, that is, still supporting our own Oxygene Pascal syntax but also accepting other variants of Pascal. We want it to be possible for someone to have a common source file as you suggest, much the same as you can with Delphi and FPC. It is possible today; we are working on the really esoteric syntax.

Our 'Delphi Island' support also allows linking to BPLs.

And we have our own IDE (for multiple platforms), as well as living inside VS.