That's a really cool idea. I don't know how you would justify it though.. Aliens are still going around in UFOs and I don't see how XCom would develop teleporting tech if not by reverse engineering alien tech.
That being said, it's an awesome idea for a new alien race. Give them specific missions, with specific UFOs that spawn, move too fast to be seen, and spend a fair amount of time landed. If you manage to catch a "landing" site, it's crawling with aliens but there's no UFO to be seen, except for a strange 1 by 1 teleport homer. That item could potentially be researched and reproduced by XCom later.
That reduces XCom's interception advantage since they no longer take place, and is a less rewarding mission than usual (maybe some Elerium in the homer, but at most very few alien alloys and probably no UFO tech).
I'll remember that when I get around to my alien mod! Nifty!