[racket] Debugger and Barrier-protected REPL?

This may have been asked and answered. Apologies if redundant.

The improvement in stateless compilation time in 5.3 has made the 
debugger a practical tool for me. (thanks again)

Is it technically feasible to evaluate simple expressions in the dynamic 
extent of the point at which code is paused?

The evaluation context could be tightly surrounded by a barrier so that 
the user couldn't change the dynamic extent by invoking a continuation 
or otherwise confuse the debugger as to where the program is halted.

To summarize: upon code halting, open a REPL in a barrier-enclosed 
thread in the interactions window.

I think this would add tremendous value.

R./
Zack