PG has worked very hard to build his brand with YCombinator. A lot of people benefit from it financially and otherwise. Naming your startup BCombinator, seems to me like naming a startup NewMicrosoft or 2Google.
If you guys have a good idea, come up with unique name for it, and work to build your own brand. Then if you hit it big, your own brand will not be diluted.
YCombinator. BCombinator. Wait. They are not associated despite just a single letter difference?
It is a similar problem as with ESL, ESL-Radio and ESL-TV. Sounds like they are an esports league, a radio reporting about an esports league, and a video streaming site about that esports-league? well... wrong. ESL-Radio has almost nothing to do with ESl and ESL-TV and is a video streaming site about ESports, while ESL-Tv streams some subset of the Esports league ESL, and the ESL is a big esports league.
So... please value distinct names to save us all a bunch of confusion.
It appears that's what they are doing if you read the whole post:
Since the app doesn't have a name yet, B Combinator will have to do until there is something more official.