This jam seems like both the Pico-8 and Tic-80 would be ideal, as they can package executables for Windows and Ubuntu and it'll be easy to keep the files under 4mb. Anyone else planning on using these engines? I'm probably leaning toward Pico-8 myself. 

I think it's been done in the previous edition of the jam and someone on reddit asked about it, but I think you're the first to confirm that you'll be using them.

I think I’ll use TIC80 as well, here is how to get it to the size limit:

To export, use the PRO build and use export linux|win filename alone=1. This will strip out the editors and keep the binary below 3MB.