Salutations!
My name is Mack Martin (as you may have noticed) and I'm the lead designer for the Stargate RPG! I just thought I'd hop in and post a response about where we are at, and what you guys can expect from a system based on 5e!
While we're currently designing the system using "classes" they aren't designed in the same way as 5th edition classes. The current list I'm using includes: Diplomat, Medic, Soldier, Scout, Engineer, and Scientist. These are obviously up for change as we go further into testing, but that's what we’re operating with now. At this stage, it's more important to use those classes to get a variety of systems into place, the largest of which is the various gear and equipment that characters might take with them on a mission. Right now we’re focused on making sure the games scaling as PCs advance is a solid engine that everything can be built upon.
All of that to say, it's very early on. But I can tell you what we’re currently working with, but understand this is all subject to change when the design meets testing.
Currently, each class only covers five levels. Once you've finished the class you choose a new one. Some of these require a previous class, for instance, an Archeologist is one of the options a Scientist might choose to delve into when they hit level 6. Alternatively, they could start taking levels of Soldier. It's a blend of multi-classing and specialization in some ways. It gives players a lot more customization than a standard 1-20 leveling system.
That's the system we’re using currently to get all the other things a Stargate game needs into place. Once we've started testing, we’re also going to test a "classless" system, although that's the sort of thing we want to build once we’ve been able to test the core engine and shake out the bigger bugs.
I'll try to hop back onto the forum to answer questions over the next few days, so if you have a specific question, I'll try to answer! Just please understand that we’re still building our working test document, so things are very early and I just might not have all the answers yet! We’ve got plenty of work to do to bring Stargate to your tabletop!