About the problem you mention with last fennel version supported by TIC, I'm actually compiling the fennel code to Lua before loading it with TIC. So I expect no problem related to versions.
Viewing post in Template for a browser game (Fennel + TIC-80)
Ah, yes I see how that would simplify things. I thought about doing this, but I figured it would be a shame if people couldn’t press ESC to see the real code behind the game within TIC after they finished playing to hack around with it. But it does let you use the features from the newest version without any hassle.