I came here just to post the same question :)
According to the info the tic-80 supports multiple progamming languages: Lua, Moonscript, Javascript and Wren.
So, in theory it should be possible to have assembly in it and I would prefer 6502/6510 assembly. Maybe this nice online console can be used by a great developer to integrate it with the tic-80: http://skilldrick.github.io/easy6502/ That would be wonderful!