First, the bad news, and the most direct answer to your question:
At this time, there is nothing like the segments in GG, and
at this time there is no intention of implementing it.
Now, the good news! The first version "Easy Building Editor" is just being polished off and getting ready for the beta testers. Lee is open to suggestions and criticisms of the building editor from everyone. When the first version comes out, that would be the time to voice your opinion on the implementation of segments! There are many around here that would like that ability (myself included), and in the democratic style of TGC, it might convince Lee to implement something similar. Take an early look at the EBE in the last Twitch broadcast and in the latest news to get an idea of how it's being implemented so far. I'ts not bad, really, just not quite "segments" in the classic sense.
There is also a Third Party Tool that allows you to import your segments into GG. I haven't used it, and don't own it, but it might be worth a shot and the price if it's that important a feature.
MAME Cab PC: i7 4770@3.4Ghz (passmark 9945), 12GB RAM, Win 10/64, GeForce GTX645 (passmark 1898); Shiny new laptop: i7 4800MQ@2.7Ghz (passmark 8586), 16GB RAM, Win 10/64, GeForce GTX870M (passmark 3598); Old laptop: i5@2.3Ghz, 8GB RAM, Win 7/64, Intel 3000 graphics