Im stuck at 3.8 as well as I had custom mods made for it. (a cool style as well) None of which work on vB4.0. Keeping my fingers crossed support for 3.8 wont end before I get everything ported over.
I'm not joking. Many small mods only require a couple little changes to make them work in 4.0. A simple change of how to eval a template, and a couple small changes to the template itself and you are good to go. You can't share the mod with anyone afterwards, but if the developer doesn't want to upgrade it, or doesn't have time, then upgrading it yourself is always an option.