I know how you feel Glen. I totally agree that this series of MBPro was a great product. Probably one of the best ever!
However, I'm a retired SVP from Silicon Valley, and the reality is that there is always an "end of life" to all hardware. Just no way for the hardware/software to be able to keep up with advancing technology. I have a host of incredible old candy-colored iMac's, original MBooks, etc. They all work great, but they can't be upgraded. The hardware has just become too "ancient".
I have a lot of respect for how Apple's products have held up over the years. I have used and abused so many of them, yet they still "keep on tickin' "
IMHO, with my knowledge of the Valley, I think Big Sur is probably the last update we'll see for these models. I'd be happy to be wrong.
Just so you know, I've got an M1 Mac Mini, 16GB, 1TB, on order and a M1 MBPro too. I'll let you know how great they are when they come in, which hopefully will be in the next couple of weeks.
Best,
Gary