In case it's not obvious, I'm trying to gauge if this indie gem will be able to run on OpenBSD one day... You might be interested with your penchant for obscure operating systems :D
We're at the cutting edge on soon-to-be-released Open BSD 6.3 with SDL2.0.8. I'm the new maintainer of that port.
The only function that's not working is SDL_GetBasePath. Seems to be used rarely and usually can be worked around.
OpenBSD's API/ABI and the libs are updated regularly, so bundled libs usually don't work (short lifetime until they would need recompiling/relinking).
If Tower 57 is written in c++/SDL2, the best (only?) chance for us OpenBSD folks would be an open-source version of the game engine (assets an still be sold). We have a few examples, like Tales of Maj'Eyal (in ports) or Eldritch (port in development)... I know that's probably not the right thing at the moment - maybe keep it in the back of your head...