I have always heard that academically they would not fit. Should that still matter?
It would matter. The presidents and chancellors control expansion.
Ideally they want a member to be an AAU member (gold standard for research intensity). And that's the rub. I did this once before, but it bears repeating. Here are the AAU members that play FBS football within the western footprint (let's call it "west of the Mississippi"):
AAU (not in a P5 conference): Rice... unless we stretch it a bit and include Tulane which is technically on the east bank. That's it.
AAU (in a P5 other than the Pac-12): Iowa State, Texas A&M, Iowa, Kansas, Minnesota, Missouri, Texas
Those are the ones that the Pac-12 presidents would rubberstamp with no argument other than some being real outliers on geography and hard to sell as a "western" university. Then you've got a couple like UC Davis (outside Sacramento) and UC San Diego they would approve but they're a country mile away from being legitimate from an athletics standpoint.
So then we go to the compromises that aren't AAU members but are at least in the Carnegie Classification as R1 (among 115 institutions with the highest doctoral research activity). Every single Pac-12 institution is R1 and it would be hard to get the presidents/chancellors to compromise on that. All AAU members are also R1. However, within that the academic side wants the schools to not be Agricultural focused because that would deviate from current research cultures, limit partnerships, and isn't worth as much money on grant cooperation.
From the non-AAU options...
R1 (most likely get approved): CSU (Ag focus), KSU (Ag focus), LSU, Texas Tech, Hawaii, Houston, Nebraska, New Mexico, North Texas, Oklahoma, Notre Dame (geographic outsider that has Pac-12 rivalries)
R2 (names we hear mentioned): Baylor, BYU, Oklahoma State, San Diego State, SMU, TCU, UNLV, Nevada, Wyoming, Utah State
R3 (names we hear mentioned): Air Force, Boise State, Fresno State
So we see how the conference is really boxed in when we have the academic component. If an R3 is a non-starter, we can forget about Boise State (the most valuable program in the Mountain West Conference). If R2 isn't even on the table, we lose a lot of the other good options.
In terms of money, athletic prestige, recruiting grounds, geographic continuity, and an academic record that wouldn't make our Pac-12 chancellors go apoplectic, the only real path forward is UT with some combination of KU, OU, TTU, Hawaii, UNM and UH to get to either 14 or 16. It's a tough spot if the Big 12 sticks together and the Pac-12 presidents won't compromise.