I have seen a bunch of '51 monitors (although certainly not all), and they roughly fall into 2 cathegories:

1. "self-contained", often with fancy features, e.g. integrated peephole assembler;
2. "core-only", where the fancy features and rather complicated GUI is accomplished on PC.

Your monitor is clearly cathegory 1. Minus is its size. Plus is that "no PC needed", just a terminal emulator. Minus is it's limited user interface.

Now you can improve on the last problem. Most terminal emulators emulate a "smart" terminal, usually VT-52 or a superset. This enables fancy features and a more intuitive user interface. I have not seen cat.1 monitor with such, all of them require to memorize "button presses", no fancy windowed outputs with simultaneously displayed memory+SFR+disassembled code as common in (DOS/console-based) emulators, for example; with a helpline on the bottom perhaps.

Would this be a too big challenge for your project?

Jan Waclawek

PS. Think also on alternative "debugging channel" to free up the default serial channel.