>> So switching to a preferred compiler would only be trivial
Apparently you haven't tried switching 150.000 lines written in Borland C++ to MSVC++, otherwise you wouldn't call it trivial.
I believe that there are 3 reasons for this delay:
1. (my interpretation) He's not only "checking" how well his code gets compiled in MSVC++, but is actually switching his development environment to MSVC++ and converting the whole codebase to MSVC++.
2. (from a trusted source) He did arrange a vacation for himself. Mountains and all that
..
3. (just a guess) mIRC 6.x was "5.9x + multiserver + minor stuff". It is time for major changes.
