If any angel(s) are looking for a niche in the incubator "market", this would be a pretty good one. Real value can be created if someone can increase the chances of success for single founders.
There are benefits to targeting a niche, common problems through the group, easier to market the incubator to a group, differentiation to other incubators.
From my point of view I would love to see a go-to place for single founders, if there's one thing we could use it's others to talk to where friends/family just don't cut it!
Lots of people like to point out Drew Houston of Dropbox as another single-founder success story (and it is!), but he did have a co-founder by the time they presented at Demo Day (if not before YC started, I can't remember which).
However, he did apply as a single-founder. Here is his YC S07 application: http://dl.dropbox.com/u/27532820/app.html
Jeff Bezos was a solo founder when he started Amazon in 1994. Employee #1 (Shel Kaphan) was brought on before incorporation, but says Jeff was the founder (http://www.geekwire.com/2011/meet-shel-kaphan-amazoncom-empl...)
Andrew Mason was a solo founder of Groupon, started with $1 million seed money from a former employer.
The single founder was Philip Kaplan (although he's not you're average single founder).
But then how would the VCs play the founders off one another?
You're either a VC or under 30.
Edit: There is clearly not a lot of gray hair on this site.
In a startup, the founders, and their relationship with each other and the company, is probably the biggest asset. If an investor doesn't like the team, he just won't invest at all.