I implemented VBA in C# a few years ago for malware analysis, and my takeaway is...well, it's a hard project. Possibly as hard as I've ever done, but a big part of that was guaranteeing bug-for-bug and type conversion compatibility and obscure language features that nobody would include today. I can't even fathom how the old folks implemented BASIC in 256 bytes of 8-bit assembly back in the day.