untested, but I think you could possibly bypass it with a malicious .inputrc binding for <enter>, although making it conditional such that it only removed a leading \ could be tricky.

In Bash there might also be a way to do something cunning with a 'trap DEBUG' hook to modify the command between submission and it actually being run.

Or you could just exec into a terminal multiplexer like screen[1] to intercept & rewrite/suppress both commands and output.

Edit: It's much easier than that.

The function:

    echo () { command echo "hax" $@; }

will still be called by '\echo test' (The 'command' prefix stops it becoming a forkbomb :)

[1] or maybe just hijack stdin/out FDs from the shell?