I have read of Merlin 55M Spitfire V's before, but I could never find a picture with a caption labeled as such. Also, official tests often state that the Spitfire LF V usually had a Merlin 45M, and the only 50-series engine Spitfire V had was the 50/50M.
besides, the Seafire III I believe, was more common with a 55M than a Spitfire LF V with a 55M. Also stated, the Seafire had the 4-bladed prop which is likely to act differently than an LF V's prop. We've also got rockets and bombs on the F/L III. Though, honestly, I'd prefer the F.III because it has a better climb-top speed balance, the L.III was more common and is probably likelier to arrive if any new Seafires arrive.
XII is surely a welcome plan, but it was made in such few numbers; I'd like to have the Seafire added first.
No need for an LF IX; we've got a XVI, though the Merlin 266 is actually supposed to have a differently tuned supercharger, having the stage kick in and kick out alightly above and slightly below respectively when copared to the original Merlin 66 according to the manual.
If a 1945 representation arrives, maybe it will be an FR.XIV? Bubbletop canopy, clipped wings, rear-fuselage fuel tank. Pretty ugly Spitfire if you ask me, but the most accurate representation of a 1945 operational Spitfire.