The member tables of 6.1.6 and 7.x are quite different. In any case, even if someone did code a cruncher for importing members to D7, you would be stuck with the current beta --- as there is no upgrade path provided between the betas.

Also, Boonex staff members have explicitly mentioned against providing third-party "upgrade paths" --- and quite understandably so, as public betas exist primarily for the sake of further debugging, and third-party upgrades could mix up things and introduce see more new bugs to the custom-upgraded Dolphins.

If you have a live site, you shouldn't be thinking about converting it to anything but a stable release of D7, whenever one becomes available.