I like your idea. In. In a TL of mine I have something similar being done by the RN to improve the KGVs after the treaty falls apart early.It's a derivative of the KGV just using the fact that it will have decently lighter and smaller machinery to good use, oh and adding a transom stern and a bulbous bow to increase speed with all the costs of the required water tank testing be solely paid for by my nation since I am of course a traitor(that this and the use of the Mark II 15" gun almost certainly will be used to improve the KGVs is icing on the cake). Oh and of course since I'm a traitor they will be scheduled to be completed in late September and early December of 1939 . Mind you methinks the 48 40mm Bofors and 20 5"/38s (with 4 Mark 37 directors for them) that they'll be equipped with from the beginning will be very useful indeed while in RN service.
As for your second idea that's just evil
And yeah I think even if my suggested design enters service through some miracle it would be astoundingly bad.