I am hoping that one model (maybe the $3000 model) will have a standard BB. I think that BB-Right is an awesome system, but I have no intentions of buying a new SRM - and I am sure that there are a lot of other people who feel the same way.
All three S5 models have BBright for best stiffness and weight.
What kind of SRM do you have? Unless it's a 68mm only system (square taper or OctaLink), with the right bottom bracket bearings & cups it will probably work in a BBright frame.
Check the BBright compatibility tables at http://bbright.net/supportingbrands.aspx to see what parts you might need to use your SRM on an S5.
By the way, backward compatibility with crank-based power meters is one of the three reasons a BBright bottom bracket shell is longer on the left only, not on the right: we respect the space the power meter uses. The other two reasons are:
- Triple chain ring compatibility (a 30mm axle needs a big enough bearing it hits the ID of the granny gear if it's too far to the right), and
- There is no structural benefit to widening the BB shell to the right: no frame tubes can get wider (FD, chain are in the way), and the shell just "sticks out" unsupported, with the curved fibers creating a poor structural load path: heavier or more flexible or both.