It"d be awesome to be able to save the state of the whole program,
which would be to save

• the whole 64k memory (maybe compressed, but 128kByte is not that much these days..)
• all registers and processor flags
• the state of every plugin
• the positions and name of every label for debugging

into a file which can then be loaded back into the emulator for further debugging.
Evenutally, the sourcecode could be saved too, for easier debugging if the code has been changed.