I really hope that they stick as close as possible to the BT rules.
However, I seriously doubt they won't abstract a lot of things, change the rules to make them easier to code, and dumb down the system for people who don't play BT. So I seriously doubt this will be a good replacement for megamek or the board game. I do hope to be wrong, but I think this will be more "Final Fantasy" with mechs than megamek with better graphics.
Writing a 3D graphics interface for megamek isn't exactly impossible, quite a few of us have done a 3D hex/mech based interfaces in the past. Megamek would need an API though, basically a way to send it all the turn code, and query everything possible in order to have a true interface. I would love to see that, and know its possible, but I neither know java well enough or the megamek code base to actually code that. Actually, since it does have a server/client communication system much of the updates are all essentially completely, there really just needs to be an API layer to the interface to allow external applications to control a megamek game.