I have done my share of games and emulator porting for N900. (Widelands, Bos Wars, Open Dune, Robbo, psx4m, uae4all, ...) It was relatively easy - just need to tweak UI here and there to better fit for "invisible mouse cursor".
Recently I wanted to port these to Jolla Phone and stumbled on a real show stopper - Sailfish OS does not support landscape mode for SDL apps.
I know that your "standard" answer is to rotate in software. But that's just PITA. I loved that on Maemo 5 the developer need not to be concerned with the device orientation. The screen dimension change was just signaled and you needed to relayout the application only. (With a cool rotation animation provided by window manager.) Or just request fixed layout to be pinned for your app. No need to rotate your pixmaps manually, translate pointer coordinates and so on. It was coded once and for all on the lower layer and just worked.
I have already spent too much time on rotating just one game and it still has glitches and weird issues. And thinking that I need to redo/reinvent all these work for each and every one pending... I'm sorry, but that just won't happen...