The HMS Hood was due for amour upgrades etc, but she was too needed to be able to be withdrawn from service. Bad mistake.
I really don't like this idea as an inclusion in the game, but it is good for personal mucking about and testing.
Most WWI BBs had extensive refits and upgrades, but the ships still essentially remained the same class. Upgrading a Revenge class to a KGV does not make sense to me. They are too different. You could suppose the the upgrade is simply a crew switching to a newly built ship, that would be a better abstraction than having a ship drydock and be rebuilt in a way that never would have happened.
The ship models system works ok for for smaller vessels, but I think battleships classes were too unique to be well modelled with this generic 10 model system. The QE class for instance is a much better ship than the following Revenge class, but this system will always define the Revenge as having higher stats. I have been thinking about whether the extra research tabs like D-Day made could be used for unique battleship models with individual upgrade paths. That would allow for far more accurate modelling of each different ship's strengths and weakness. The techs in the capital ships tab would unlock nation specific unique battleship classes as well as allowing unique upgrade paths for every battleship class. It would be a tricky mod, but would be possible and work really well.
I like the nicknames given to HMS Renown and HMS Repulse. They were in drydock etc so often they were called HMS Refit and HMS Repair. British ships sure had great names too,