There is no prerequisite to have a "stable tech infrastructure" -- shoot, there's no prerequisite to even have an actual product! -- for admission to YC. pg has made it pretty clear that YC selects founders, not necessarily ideas.
And for those that have a proof-of-concept running on some other provider(s) (AWS/Rackspace/Google), it would be a huge boon to be able to migrate and scale using Azure and the $500k credit.
And for those that have a proof-of-concept running on some other provider(s) (AWS/Rackspace/Google), it would be a huge boon to be able to migrate and scale using Azure and the $500k credit.