I would think that a modded minecraft server would be great addition to this network of games. Modpacks that are extremely popular right now are the following: Direwolf20 1.10 SkyFactory 3 FTB Infinity Evolved Or if you want to try a lite modpack FTB Infinity Lite If you need to know how to add grief protection and permissions, I have links to each one and I have "some" experience with it.
Server wise, Agrarian skies is a little hard to setup and it also causes a lot of memory usage because of the hardcore questing mod which doesn't really work well with multiplayer. For a major server network, it's not a good idea.
@irritatingness said he didn't have the time and such to manage a modded server unless thats changed I don't see this going anywhere Neutral.
By manage do you mean griefing, managing the plugins, and setting up configuration on what items should banned and whatnot? What do you mean 'manage'. After you setup the server, it should be pretty simple to manage it, all you have to do is setup an auto restart script which most hosting services have by default and have moderators that have griefing and plugin/configuration experience watch over it. Prism and Coreprotect mysql logs are easy to look at and can be set so certain people can access the logs and nothing else so they can do their jobs for griefing. towny can be used to stop any sort of direct griefing for mods, and etc. Yes, I can see it being a bit hard at first but once you get people who have experience, they can work together and most of the time you only need 1-2 at a time to watch over the server, and if nobody is on, they can get notified via the forum by other members and they can easily check chat and mysql logs.
Also lets factor in resources and time to run a second server. It's a good idea, but...I don't know if the people involved right now could handle two servers. That said, mods are <3 and hopefully in the future we can have a modded server. Mod pack has to have Chisel and/or Carpentry or -1, though.
skyfactory 3 has chisel and bits, as well as chisel I believe, and it should have carpentry, I'll have to double check
As it's been mentioned previously, we don't really have the resources at the moment to run two servers. If SMC is successful after a good period of time, and we've gotten to the point where we're not constantly changing things and fixing stuff, it could be a possibility, though ultimately up to the owners. Basically, not any time in the near future, but I can't say it will never happen.