After 3 different cancelled online dealer orders and a fourth one issuing a tracking number but neglecting to actually ship my package for 5 days (huh) until I contacted them, plus a subsequent weather related transport delay, I received the USB hub and cables yesterday. Completed the install between last evening and this morning (firmware update done previously)...not at all terrible, and nothing thankfully broken or damaged.
--tried the shortcut to access the hub via the footwell as I don't have huge hands, but tore the crap out of my forearm and have a nice big bruise as a result. I could get to the hub and easily removed the connector/existing USB cable, but could not release the tabs at the same time adequately enough.
--the add'l parts for the full removal were not a lot of extra work to complete, at least with the official removal instructions and guidance from those who came before me.
--Could not for the life of me get the two internal wiring connector mounts off of the rear and center console frame parts, so fudged that by pushing the rear console back as far as possible to allow the upper part with the hub to come out enough to get to the original hub.
--Got irritated and just broke off the tabs on the hub to get it removed. (wink)
--I was able to get the new USB cables from the CMU area down to the hub by simply dropping them off to the right, where I could see then them in the right footwell area, and then continue to route them around and behind into the hub area. Didn't need to use my fiberglass wire fish at all.
--Took the opportunity with the decoration panel off to re-do my ProClip mount, which I noticed was installed incorrectly and upside down.
--Tested before reassembly, and the CP prompt showed up and it worked.
--Everything went back together properly, although the center panel around the screen was slightly difficult to get back in place--you kinda have to flex it outwards to get the tabs to properly seat in both the top and side bottom areas.
--Had a minor heart attack for a moment when I first turned on the car again. The electronic emergency brake apparently needed time to reset, as it would not turn off and just flashed at me. After waiting a bit and turning the car off/on, it again worked as expected.
--Checked the errors and deleted the one noting that the headunit had been removed (had to move the car during disassembly with the CMU out).
Very happy with CarPlay, in particular since my Mazda Nav maps subscription expired a month ago. Pandora also works more reliably via CP than through the car's system (makes sense since it is direct from the phone, with no go-between as with the MZD Connect Pandora app).
Also noticed how much easier it is in general to release the various wire harness clips in this car versus my 2010 Mazda6, in particular on the CMU where navigation room was limited. The clips have much easier to release designs now.
Much thanks again to everyone's input to date on this, and a big thanks to (Mazda3 Revolution's) ASH8's tireless support of this effort and all the help provided.