I pre-ordered so I read about it in their updates/blog, but they have been actively working on getting everything mainlined.

Search for "Suspend-and-Wakeup on i.MX8MP" and they mention it briefly, they went more in detail about it in previous blogs though: https://mecha.so/blog/mecha-monsoon-update

On top of working with the chip manufacturer to get the cpu side mainlined, they've also been working with the contractor firm "Igalia" (who've been hired to work on mainlining and upstreaming a bunch of open source projects the past few years) on getting the gpu drivers cleaned up and "mainlined" as well.

Honestly a lot of the work they've been doing will benefit other linux on arm projects, especially mobile. I agree with you though, if a project isn't putting the work in to get everything mainlined, then its not worth considering (atleast to me). I wish Ubuntu touch and sailfish all the luck in the world, and respect the work their doing, but for me its not a option.