SpritesMind.Net

Quick question, can you see any potential barriers to making a bridge board for this devkit that allows the Master System to be controlled in a similar way to the Mega Drive? Obviously it'll require new firmware and a new monitor program, but software issues aside, any barriers you can see?

Certainly feasible. The SMS's Z80 could be made to do breakpoints and single-stepping using the RST instruction. But it would be more work because you probably can't just build a Z80 GDB and use that. But running and cycle-tracing code should be straightforward with very few changes to the VHDL.