I wasn't impressed that the plan only mentioned lithium ion, at least from what I've taken in during the last 24hrs. Stationary battery apps have tended to be sealed lead-acid, and much cheaper per unit of storage. The folks with both PV and batteries probably know this best.
Locking in to Li-ion is just a mistake. Better and cheaper battery technology is coming before the gigafactory even starts production. Elon and partners will be making a big mistake thinking they will be able to undercut the competition's costs. Hopefully, they will realize this before too much longer.