With RISC-V, it is reasonable to expect multiple vendors to provide CPUs. There is a very good case to expect non-backdoored chips.
That's true, but the way they do that is in a way that requires minimal changes. In terms of the management engine, that means not including AMT module (software) but keeping the rest of the ME (hardware). After all, it also does some essential things like power management and the bootloader. Removing it completely would also mean re-implementing the essential functionality.
The best you can hope for if you want to use mainstream parts is something like me cleaner where the management engine is only there for the boot, but is disabled afterwards. Something without an management engine would certainly possible, but would be limited to niche products like the librem.
I don't share this forecast. I think many private customers would view a machine without the ME and it's capabilities as a plus for a product when the marketing is done right. Especially since most don't care for the capabilities.
A lot of people say they value privacy, but when push comes to shove, they'll willingly trade privacy for convenience and cost. See: any facebook/instagram user, or iOS users who use google maps. iOS/Mac is marketed as the private phone/computer, but their market share shows how little consumers are willing to pay a premium for privacy (except in the US where iOS share is surprisingly high). You can try to convince consumers otherwise, but in truth, a management engine with backdoors/0days isn't really applicable to most consumers' threat model. The risks from social engineering attacks or unpatched software is a much greater threat.