YC has never required you to live in the US beyond the 3 months that the program runs. They strongly recommend it, but there are a handful of YC companies headquartered elsewhere (with the largest contingent in and around London).
2) Short of bussing down to Mexico and flying home from there, how would one avoid sexual assault at the hands of the US government after the program ends?
3) Whoever solves this telepresence issue for problems like this once and for all will make a mint.
2 - I've flown in and out of the US numerous times this year and have yet to be "molested" or even go through millimeter wave scanning. Even then the radiation dose is minuscule. You'll get more exposure to radiation on the flight itself than in the scan. Don't let your fear rule you.
3 - Telepresence isn't the problem; the 8-hour time difference is. Technology will not surpass this unless one side becomes nocturnal
I routinely spend two months a year in the US, and have never had a problem with the IRS over this. When I raised the issue with an accountant he bust out laughing. "Patrick, if the only refrigerator you own is in Japan and turned on right now, this is not a close call."