Having a hypergate won't allow you to do anything you can't already do. You wanna March an invading army through a hypergate and onto an enemy planet? Cool. Sound cool, looks cool. But in Chaos terms where matching armies and fleets magically show up at the same time anyway, using a hypergate doesn't actually get you anything new.
The closest thing to a Hypergate on Chaos was something that I made. A starship that can spawn a wormhole and use it as a GTFO button for abandoning a thread. I had to jump through a lot of hoops to clarify that the "practical" speed of travel via the wormhole was no different than traveling via Hyperdrive. It's just a bit cooler and entirely unpredictable in terms of destination.
I think that, regardless of hypergate remaining banned or not, that's all you'll ever really get out of them. A slightly flashier version of what you already have.
And in terms of mixing restricted materials... I'd honestly just propose yanking alchemical/whatever stuff off the list. Most of the effects gained through that stuff are entirely achievable through "technological" means. Hell, you can even get some similarly crazy effects from 'Vong bio-tech (which I'm surprised isn't right up there with Alchemy on the current list).
Alternatively, you could just have Tier 1 and Tier 2 restricted materials. No Tier 2 restricted materials can be mixed together. Any Tier 1 restricted material can be mixed with a single T1 or T2 restricted material. But only at Unique levels as Tech only. Or something stupid like that.
*Shrugs*
Now that dev threads are gone, it seems like it's mainly about denoting what production rating is appropriate for the submission. If you end up changing things a bit on the RM front, it could lead to finding a new benefit to working for a tier 6 workshop.