I do predict sanctuary to be laggy. I know on alioth i have been building and have been able to keep my lag down by spreading my buildings out on different hexes, i even spread out my ships so they are not all located together to create lag. Now i am being pushed back to sanctuary , all my buildings and all my ships will be all concentrated onto one tile. And i hate to break it to you, my tile is very close to a market there. So lag, lag , lag.
I think a lot more people will be returning to sanctuary than you think. For now a lot will go to space, but if taxes start there, then a good number of them will also go to sanctuary. Sanctuary will be not only for new players, but also any casual player that can not predict his/her schedule will be forced to stay on sanctuary.
I have already started removing my buildings and will continue planning on how to move/relocate. All the players in one org i belong to are also moving to either space or sanctuary not one of them plan on staying on alioth. Another org i am in are all pretty much staying in place, so it sort of depends on your play style and your real life situations. But dont be surprised if sanctuary becomes a lag fest and alioth sees great improvement.
So if you are flying over sanctuary and your screen suddenly locks up, be sure to wave "Hi" as you will probably be over my one hex with all my buildings and 20-30ships.