IMO, it seems like it would be really difficult for Tulane and Memphis to commit to this new conference. A few of the challenges are:
1. AAC departure. The current conference requirements say a departing school needs to provide a 27 month notice, as well as pay a $10 exit fee. The thing that sticks out most is the 27 month exit fee, since the PAC would need the new schools to be part of the conference sooner than that. It's likely the conference would let them go earlier, but at a higher exit fee. In the last round of exits (Houston, etc), it was $18 million per school with the shorter notice.
2. No known media deal for the the PAC conference. The current AAC deal gives each school around $7 million per year, so they would have to give that up, for an unknown amount as part of the new PAC deal.
3. Travel. Currently, the 4 of the 6 schools in the new PAC are on the West coast, with Boise State not being too far from the west and CSU being the most central. Assuming that the PAC adds Tulane and Memphis, you'd be logging a ton of travel time and expense. It isn't terrible for football only, due to the lower number of games, but it would definitely add up for all other sports, which is what I'm assuming the PAC is looking to fill the spots for, not football only. It wouldn't be as bad for the other 6 PAC schools since they're mostly regional, and they would only have to travel to Tulane and Memphis periodically, but Tulane and Memphis would be making those long trips for 6 of their 7 roadtrips.