SDSU could get an invite if:Yeah, SDSU + Memphis (or Fresno?!?) adds... blech. I don't think that happens.
I think SDSU only gets in if:
CU, UA, ASU join
AND EITHER
UU absolutely refuses
OR
the TV money says SDSU > 2nd team in Utah.
I think if any movements happen at all, SDSU is much more likely to end up in the PAC. Either as part of a 2 team add to get back to 12, or as part of a larger add to backfill teams jumping to the Big12 (or B1G).
People in San Diego/SoCal realize SDSU has an athletics program with a football and basketball team
AND
Those people start to watch the games in significant numbers.
I get there's a sense that SDSU could be valuable because of the time zone, large local population, or adding a travel partner for ASU/UA/UU. The reality is they simply don't have a large fanbase and joining a conference with a bunch of schools from states that a large portion of the local population couldn't pick out on a map probably isn't going to be a gamechanger. The local culture simply isn't attuned to college sports. Until that changes, nothing else really matters. As for being a travel partner with ASU/UA/UU, the drive times are 5/6/11 hours.
If there's a situation where 1/3/5 PAC schools are ready to make the jump, it makes more sense for the B12 to either leave one behind or just roll with an uneven number. They'll have an good chance of being able to pick up some ACC schools in ~10 years to even things out. Adding SDSU now just to get an even number would be a permanent solution to a temporary problem.
SDSU's most likely move is to the PAC after further defections. Just like the B12, SDSU is not likely to help the numbers unless the PAC needs more members to stay alive.