I've done a bit of NES programming and really enjoy trying to cram stuff into such a tiny system.
One benefit of developing games for these old systems is that they are not moving targets. For hobby programming, you probably don't want to keep testing and recompiling old stuff to keep up with OS updates.
Even better, you'll have a small army of emulator developers making sure your games will work forever on every new platform. That includes browsers, since there are Javascript emulators for many systems. If your games are particularly tricky to emulate, that's no problem. They will probably be added to everyone's test suites.
One benefit of developing games for these old systems is that they are not moving targets. For hobby programming, you probably don't want to keep testing and recompiling old stuff to keep up with OS updates.
Even better, you'll have a small army of emulator developers making sure your games will work forever on every new platform. That includes browsers, since there are Javascript emulators for many systems. If your games are particularly tricky to emulate, that's no problem. They will probably be added to everyone's test suites.