I found a drawing for the Novato downtown platform, 270 feet long. The rail vehicles are 85 feet long. That doesn't give much wiggle room, 7.5 feet at each end.

Since there have been many complaints that service needs to be more frequent, the first thing to do would be to do just that. When frequency gets high enough to be limited by single tracking one would add more sidings, or extend those already existing. However all of this is pretty far down the road. First comes Larkspur Landing and then Windsor. Not too difficult. Beyond that gets more expensive and the potential ridership becomes less.

It will be interesting to watch: YIMBY versus NIMBY.