My personal thoughts is no, it won't. I'm guessing that they didn't add SF to the Premier group for a few reasons (which still exist and will still exist even after the new park is opened.)
First, with 1K rooms, that means possibly another 3K-4K people with EPs. There are already 2.4K rooms (between the existing 3 Premier hotels with EPs. That means 7K-10K people (or possibly more) when hotels are full with Unlimited EPs. Don't forget they also want to sell EPs to the general public and the top level AP comes with an after 4pm single use EP as well. I'm guessing they won't want to dilute that benefit too much.
Second, I think there is a market for hotels with similar in-hotel amenities, but at a lower price point (i.e. Preferred hotels). If they move SF into the Premier bucket, they would also need to raise the rates accordingly. They would no longer have a hotel that is very similar to the Premiers, but without the added cost of the EP benefit.
My guess is once the new
Epic Universe park opens, yes, they will then have an opportunity to add another (maybe more) hotels to the Premier bucket. But even then, and I'm just guessing again, they might add one of the new hotels going up around the Epic Universe park to the Premier group, not add SF to it.
Third, SF and RPR are very similar hotels in a number of respect even down to the theming and location. The big difference being SF is much newer than RPR. (Yes, I know it doesn't have a lounge, but that could very easily be changed, even today, if they wanted to.) My guess is if SF were to be a Premier hotel it would have started that way and they would have then removed the EP from RPR to keep control of the number of Unlimited EPs being used throughout the parks. Since they didn't do that when the hotel first opened, I'm guessing they wanted to the "newness" of SF to provide a bit of extra incentive for folks to stay at SF instead of one of the existing 3 Premier hotels (especially RPR.) You essentially have a new, improved RPR without the EPs at a lower price point to stay at where if they switched the EPs to SF, RPR might have a larger drop-off in stay traffic.
But all my thoughts above are my own and I could be very far off from their reasoning and what they will actually do.