Everyone always talks about Miami being El Al's next US destination, but I think there are a few destinations that could potentially see El Al service in the future.

Miami - This is the obvious one that everyone talks about. The Miami metro area has the 3rd most Jews of any metro area in the US (behind NYC and LA). Along with this, there are currently many Israelis who travel to MIA/FLL by connecting to B6 at EWR, JFK, or BOS or AA at LHR, MAD, or CDG. Personally, I think that the market is big enough for ~6-7 weekly flights.

Philadelphia - AA recently dropped its PHL-TLV daily nonstop, but the flight did have a lot of local travelers. With a pretty sizable Jewish population and considering the city had a nonstop until very recently, I think the market could support ~4 weekly flights.

Chicago - The city has a pretty big Jewish population and is a big business city. Currently served via B6 codeshare from JFK/BOS and AA codeshare via LHR. I think the market could support ~4 weekly flights

Washington, D.C. - The DC metro area has a pretty large amount of Jews, and is in the top five of any metro area in the US if Baltimore is included in the count. The government could also demand a lot of traffic. I think the market could support ~3 weekly flights.

San Francisco? - I don't think the market is big enough for both UA and El Al, and I have a feeling UA will eventually increase its service from 3x weekly to 4-5x weekly. With that in mind, I think it is unlikely El Al will enter this market, but I wouldn't be surprised if it starts codesharing with UA on this flight.

As a side note, I wouldn't be surprised if Boston is upgraded from 3 to 4 weekly flights in the future. I have heard this flight is doing well and benefits from B6 connections.