I think they would fit I replaced the 510 with the Cisco 510 and moved the battery tray over a little more since I took this picture. I don't have 21700 batteries at the moment or I would tell you if they fit or not. Sorry took so long to answer.
Yeah I was looking at getting the turnigy 1300 bolt 4s for the DNA250C I want to build as soon as the boards come out. Also was looking at the Maxamps 1850 4s as well.
In that interview with pbusardo john himself said "It will be out by Christmas easy". But we all know we can't make these things happen. It would be nice to at least have specs and a release date by now though.
Alpinetech GXL
Dual 20700
I just built this today I really like it. It went together fairly easy. I used a varitube V2 510 but I think I'm going to order a Cisco 510 and replace it. I don't like The varitube V2. Also I love this board. I really hope they come out with a 250C.