I can get Cells to sorta work with Renoise 3.x by editing manifest.xml and upping the API number. Renoise will then allow me to enable the tool.
But I get a Lua error if I try to start it. Now that I know some Lua I’m tempted to poke around and see what can be done to make it play nice with 3.x, but the lack of proper documentation is putting me off. I’ve yet to do anything useful with Cells in 2.8.
The Cells manual seems more like an FAQ; it describes assorted details but lacks any kind of “Getting started” help. It seems to assume you already know what it does and why it does it.