I've always wanted this! Using different types of weapons from Balkon's Weapons Mod in the Survival Games would add a new dimension to the games, so it's not entirely tier based, like it is, and it's very difficult to kill someone with drastically stronger armor and weapons. But I can see it being a huge RAM issue, so maybe one or two tekkit mcsg servers if anything?
If you're going to have only one or two servers, then that would work very well, since, like James.D said earlier, only a handful of people would download a new client to play mcsg. Though there is also a chance that all the variety would make more people attracted to the servers then initially planned, and in that case maybe some more servers could be opened up.
Either way, it couldn't hurt to open up one tekkit test server to see if people would go for the idea. (Or maybe it could, I'm not great with computers -_-) and depending on whether or not the server gets traffic as much as (or preferably more than) the standard mcsg servers, we can go from there.
I'm not suggesting you go with the idea right now without thinking about it beforehand, and weighing all the possibilities at hand, but if you were to do it, this would probably be the best course of action. And now, I'd like to point out how great a tekkit mcsg server could be! ^_^
First! New types of weapons! Imagine having to choose between a sword or a spear. You can throw the spear! But then your enemy will get it. Flails can be used for surprise sidesmashes and such, and, oh god, muskets. Beautiful muskets. Muskets can be used for a pretty reliable one-hit-kill (so maybe nerfing is in order), and if someone rushes you, you can whip out your BAYONET! Oh yes. Stabbing and shooting.
Second! Jetpacks! Imagine finding all the complex materials needed to craft them in a chest, and flying all about Map 2. Brilliant, isn't it?
Third! Item complexity! Some people who aren't familiar with Tekkit crafting (like me :3) might not even know they have all the materials needed to craft a game-winning item, and prance around with a wooden sword instead. Then, they're killed, and the new, more worldly player could make better use of items at hand, and seemingly useless fuel cells found in chests could be used for something great!
Sorry this is so long (it would be longer), but I have a lot to say on this topic, and actually a bit more to say negatively on the idea as well, but then I realized that I'm G33king out, so yeah.
Have fun with the above wall o' text.