Totally reasonable to ask about. The difficulties into doing this are pretty technical, you had to maintain on your servers a fork of development for any major release, then give to players the ability to switch back to previous versions. 7DaystoDie do this, for example, you can pick the Alpha you want to play on it. In Conan, will be a bit more complicated due the official servers and the private servers, not only the one hosted on external services but also the (limited) server you use in SP. Still, this is not impossible to do. For Mods, will being complicated, because the Modders had to update the Mods at the last version of the DevKit, and in this case they should maintain remote repositories for any mayor version of the game. I think the problem will come more in this situation, Modders do these mods basically for passion (or for little money on their own Patreons/etc), and this will make the things very complicated for them first.