Same thing is being done for Rollercoaster Tycoon 2 right now, though it patches the original .exe to use a .dll file that override the original ASM addresses and calls with C functions. I really, really like the maintainers gradual replacement approach.
Wow, thank you so much for mentioning this project (never heard of it before). I absolutely loved RC2 when I was younger and if I can get this to run with the GOG version I will be certainly do my share to bring it back as open source.
https://github.com/IntelOrca/OpenRCT2/