All good points, here's the deal...
First of all, saying "why not FMX" is like saying "why not Z102?" Just like Z102 is the only Top 40, FMX is the only Active Rocker. And either one of them are expendable, since if either goes, it will leave a gap for someone to fill. I can almost garuntee that if Z102 goes, either 97.3, 104.9 or 100.3 will adjust to pick up the format, and I bet it would be a race to get there first (smart money would be on 100.3, which is a Mix96-1 clone). Similarly, if FMX went (which it will not becuase it has a loyal following and is second to KLLL in years as a heritage FM), Rock 101.1 would almost certainly default as the Active Rocker YESTERDAY. So anything can happen. I don't see them flipping Z102, and since Jack would compete againt number 2 station Kool 98, I don't see Clear channel Lubbock picking up the format.
Second, KJAK is owned and run by a devout group of religoius broadcasters who believe in religion and community. It too has a loyal following and provides all of the broadcasts for the local highshool sports in the Lubbock area, with strong ties to KRBL, LVT and KJDL. Since the station calls itself "KJAK," it is unlikely that we could have a JACK labeled Variety Hits station in the Lubbock DMA without some coaxing from Sparknet or perhaps a donation (since I believe KJAK is a non-profit).
All that said, I DO think that Lubbock is the next market to get a Bob/Mike/etc Variety Hits station. It just won't be on a Clear-channel station, and it won't be named JACK. So that narrows it down, and you can fill in the blank of who the likely candidates would be.
Than again, I've been wrong before about knowing JACK...