Lyft has "Plus" which as far as I can tell is very similar - http://get.lyft.com/plus/ (both services are mid-sized SUV's, not vans, and claim to seat 6)
Lyft Plus is more or less a novelty and doesn't match UberXL in terms of availability. In Seattle you can get an UberXL very easily while Lyft Plus is nowhere to be found.
I could say the same to you! SF is not representative of Lyft's service in the rest of the US at all, being the location of the headquarters. Same for Uber in SF.
Assuming people accept this, van availability would be a critical component of the competition in this field.