Not knowing what YC actually does, my first 2 thoughts were: O-1 and J-1 Visas (certainly there could be other solutions)
O-1: Typically I would think of athletes/entertainers, in the US for competition/show/tour/etc... It may not apply to some young founder getting into YC who has no other track record of success; however, YC/Tech are politically connected so the mere fact one is accepted into YC, it might = extraordinary ability (in the eyes of the Gov. anyway)
J-1= I personally have never gone down this path in my legal career, so I am not 100% sure, but it is possible YC is part of an exchange program...if not, they should set up their own business education exchange and consider this especially for their fellowship program...boom legal hack (and except the fact I just gave it away, I could have applied to YC with the idea of hacking the legal system to get more visas for foreign founders joining US incubators...YC application hack)
I think J-1 would be the most legally correct (IANAL and all but I have some J-1 experience). YC should be able to bring founders on board. Since J-1 is for education and the program is basically an education.
J-1 is also quite openly (ab)used to bring employees over who do not qualify for a H1B or O-1.
Only important thing to remember is to pay the J-1 "student" otherwise they are (depending on origin country, but most I think) subject to a rule preventing said person from returning to the US within two years.
I think J-1's are 18 months max. Plenty of time to get a business up and running. By that time if the founder is successful (e.g. take on more investment) they could probably employ themselves with a H1B or E-2 ("investor") visa.
But I'm sure the J-1 has a bunch of issues concerning founding legal entities - this part I have no experience or knowledge of.
No, as a founder you can forget to get a H1B visa, even 2 years in. Unless you have a legit board of directors and you can demonstrate you could potentially be fired, they will argue that you started the company to employ yourself and get yourself a visa that way.
We applied through Intrax (http://www.intraxinc.com/global-internships) and the cost for the 18 months was a little over $2k. Considering it also includes medical insurance, I'd say it's a pretty good deal.
The main requirement is the US company needs to have at least 25 full time employees -- not sure if YC qualifies.
O-1: Typically I would think of athletes/entertainers, in the US for competition/show/tour/etc... It may not apply to some young founder getting into YC who has no other track record of success; however, YC/Tech are politically connected so the mere fact one is accepted into YC, it might = extraordinary ability (in the eyes of the Gov. anyway)
J-1= I personally have never gone down this path in my legal career, so I am not 100% sure, but it is possible YC is part of an exchange program...if not, they should set up their own business education exchange and consider this especially for their fellowship program...boom legal hack (and except the fact I just gave it away, I could have applied to YC with the idea of hacking the legal system to get more visas for foreign founders joining US incubators...YC application hack)