[cmrdporcupine]

cooperative multitasking, no memory protection, can't take advantage of multiple cores, and very much tied to the ARM architecture?

[pjmlp]

Has Haiku already improved the crash friendly in multihreaded code experience, and software rendering from BeOS?

[memsom]

Yes. There are ports of Qt 5 for example, so you can avoid the BeAPI layer and write code that is portable. You shouldn't, but you can. The Qt/QML code is standard and all the threading and BLooper/BLocker dance is not a "thing" when you use it. But, these days, multithreading is a lot more prevalent so I don't think modern programmers have such an issue with it. I write multithreaded code all the time.