As BorIDE progresses...

[boriel]

There's something alike, called BASIN. Unfortunately, it's closed source, so we can't see how it works.
I'm thinking on two approaches:

1. Using an embedded (or even external) debugger, using a Z80 emulation library (or using a C code for a Z80 emulation).
   
2. Creating my own interpreter, so it will interpreter ZX BASIC language as an scripted and debuggeable language.

2nd approach is my favorite, seems it's multi-platform and could even allow using ZX BASIC "scripts". :!: