To add a more recent report from T2 - the kiosks are definitely open for business for Americans transiting through MEX. A new bank of probably 20 of them has been installed between the foreigners and Mexicans queues for immigration.
Bizarrely, despite epic queues in both the foreigners and Mexicans queues when we passed through, the kiosk area was completely empty with nobody using them. An agent was physically blocking the entrance to the kiosks. We walked up to her and asked to use them, and she cheerfully waved us in after seeing our passports; from there, it was relatively painless. No idea why they aren't aggressively asking people to use the kiosks yet, but I'm not complaining if it turns into a de facto fast lane...
The kiosks operate very similarly to Global Entry; you'll need to provide all of your fingerprints on your first usage, and then future visits just validate one hand. The passport scanner can be a little flaky, so much like Global Entry or NEXUS, you may have to try a few kiosks before you find one that works if your passport is even remotely warped or bent. There's also a convenient option to process as a family at a single kiosk if you want to go that route.
The best part was that there was almost no queue to exit immigration once we had our confirmations. The immigration agent at the desk simply reviewed the paperwork, stamped our passports, and tore off the receipt - easy as pie.
A side note: if you see a queue to go up the escalators for security screening post-Customs, don't panic. At the top of the escalators, you're immediately dispensed into the security screening - there's no additional winding queue upstairs. We bailed on the pre-escalator queue to go landside and enter security from there, and while that worked fine, it probably wasted a few minutes over just staying in the transit inspection area.
We'd heard rumors of upcoming changes making intl-intl transit not requiring immigration screening, but that certainly doesnt seem to be the case - at least not yet. But the new kiosks make it a lot less painful, other than the wasted passport space.