Yes, we still have a higher bar for single founders, because it will be harder for them.
We both know quality developers would LOVE working for a YC startup and it should be no problem hiring someone as a co-founder IF you know how to pick. Now, of course, that co-founder was not born in the same hospital as you and you might not have that super SyFy connection as super old time buddies but will that lead to a startup failure?No,I don't think so.
In fact I am willing to bet that even a non-technical single founder (ye, we don't like them) with no experience what-so-ever, can handle YC application process. How? Raw/natural talent, cleverness, cunningness etc. Qualities hard to measure and observe, no doubt, but most valuable. If you can get a founder like that, there should be no problems in the future. Going "by the paper" is not always the best choice.
EDIT: And in all honesty the YC Application form is cleverly made to target a specific group of people, eliminating a huge amount of talent and in some points minimizing innovation.