but is it going to be the same in, say, 15 years?

You would think that by then either the Rust experiment has failed or the project has gained enough experienced developers such that maintaining such large refactors is feasible beyond heroics of the RfL folks. Either way it would be unlikely to be a problem then.

But in the meantime, how is the Linux project meant to evaluate what the maintenance burden is or wether the benefits outright the costs if the kernel maintainers doing the RfL work are being repeatedly stonewalled?