I didn't know this and it's pretty surprising to me. In any case it's all the more reason I don't think it changes anything here. I'd be really shocked if they outright dropped support for non-T2 Macs at this point in their lifecycle, especially if they were selling new machines a year ago without the chip.
It just stands to reason that macOS would become more dependent on security hardware over time and they would fudge whatever they need to separately in order to keep the older models working through their support life.
I've no insight into macOS internals but I'd suspect that by now there's some kind of software T2 chip in the kernel for these older Macs that performs as much as possible of the same function minus the tamper protection and hardware acceleration - and that they're pushing updates for that separately.
You could buy a brand new iMac up to August 2020 that lacked the T2.