I believe it's because that's about how far out network planning and selling tickets go.

They made adjustments overnight after the -8 was grounded. It’s not hard to stub out a 700 for a -7 and change the seats available to sell from 137 to 150.

Swapping out 2 aircraft that are airworthy and already on ones operating certificate is night and day from bringing a new aircraft onto a certificate even after the aircraft is certified by the FAA.

Maintenance procedures
FADAP/FQAP install and setup
nav, maintenance settings in FMC, ACARS/CPDLC registration
RVSM approval
insurance for various regions
wifi?!?
satcom

Just because these items are bolted to the airframe doesn’t mean pilots can flip a switch and have them work. Getting ACARS reg/servers SATCOM SELCAL insurance etc take a lot of effort to push through. If you’ve ever put an airframe on a certificate you can appreciate the headache a working with the authorities.

and that’s IF the government isn’t shutdown 4Q of a midterm election year

I agree there's a lot of work to do....but just because network planning has seats for sale 6 mos out isn't the reason we wouldn't fly it until then. Like I said....things can happen overnight in that dept. The list you wrote takes time.

MAX-7 will be the next assassination victim... er I mean the MAX-7 will apparently commit suicide at the exact time the video surveillance system is glitched out. It's well known that MAX-7 is still in protective custody because it may or may not have incriminating information. It won't survive, let alone get certified. Embarrassing or incriminating, it's too late for it to matter. Perhaps we'll gift all of the completed airframes to a country we've recently befriended through firepower, because sending flowers isn't really enough and we found out that pallets of cash isn't effective. So maybe they'll get some uncertified airplanes that know too much. They'll need a name change as part of the witless protection program...

You...uhhh...okay over there?

*UPDATE*

I asked a PHX mechanic about the mystery aircraft...turns out it's a Max8! I first saw it from an angle and a distance. Really seemed a bit shorter, but oh well. He said it is slated to be the newest logo jet, but did not know why it was stopping in PHX on the way to the paint shop.

It may have been in town for install of the Honeywell Surf-A system. Honeywell and Southwest ran live tests, possibly out of Topeka, using their E170 and a SWA 737.

Whats this Surf-A system?

Are we supposed to know what that is?