As for sdcc: while in theory I agree with everything that's been said about how someone else might pick up the slack if the maintainers get bored or distracted, in reality, how often does that happen?

I have only been with SDCC for the last two years so I picked up where others left off.

However, it is still not possible to use the _at_ keyword for constants in code space, which is one "feature" I'm missing.

This is on my wishlist too, but I postpone implementation until after the 2.6.0 release. And in general bugs come before feature requests. But you can always add a comment to a feature request stating you need it too. This might increase the priority.