My hope is that Motorola will be very successful with that. GrapheneOS currently has half a million users and growing. The more users it gets, the more interesting it is for manufacturers to actually consider it.
Google being Google, if Motorola gets a relatively cheap phone to run GrapheneOS (the flagship is quite expensive IMHO), I think people will flock away from Pixels (I definitely will, and I will tell everyone and their dog that they should when they renew their phone).
That is a total install base right? Unless all 500k of them are upgrading yearly, this number is miniscule. You are underestimating the R&D required to put out a new phone each year only to have 30% (high estimate) of users buying it. That's 150k devices, which is not worth any volume.
Also I am genuinely interested: is it that hard to meet GrapheneOS' requirements? Feels like it shouldn't take years of R&D for every new iteration. And also that it's about getting the right deals with the suppliers, which is not really an R&D issue?