Oded,
I could be wrong, but I don't think Zero will be getting rid of the FX model anytime soon as it covers both the entry-level and off-road portions of the market (which is pretty good for them IMO).
The 2017 FX is offered with 3 battery options: the 3.3 single pack, 6.5 dual pack, and 6.5 'mini-monolith' single battery module. I was told at the 2014 MC show in Florida that Zero will support the modular packs for at least 7 years after purchase, and as many of these are still in use in the military & police fleet bikes, I think the separate modules will be around for a while yet (they're also the building blocks for the bigger batteries).
Just FWIW, the Alta is 267 lbs (45 lbs heavier than my 'MX', 22 lbs lighter than the '17 6.5 FX) and didn't really feel much heavier than my bike in a straight line. During cornering it probably will, but I didn't get a chance to do any of that during my 10 min. ride.
Your bike's looking great!
Ray