Rating flights is a very tricky business. Airlines already have some dodges to get around automated reports of things like on-time percentages (for example, if a flight is chronically delayed they can change its flight number and that will wipe the performance history of the flight on several trackers).

And rating the aircraft itself is wading into really dangerous territory given aircraft swaps and mixed fleets. For example, American's 777-200 varies depending on refit status: some are 9-across in economy, but the new configuration is 10-across with narrower seats. You wouldn't want to book based on a review for the old config and wind up jammed into the new.

So while it's nice to offer as a gesture, I don't think it's going to be particularly feasible/useful; the data curation necessary to make the reviews accurate won't just be hard, it'll be essentially impossible.