Sounds like the RN is building a (slightly bigger) Anzac frigate. Big gun frigate, with a decent hanger and aviation and some self defence. Wack on harpoon and its a decent combo.Consideration as a possibility, yes - but it's not (at least publicly) been specified as the chosen gun, any more than 76 mm, & nor has the top speed been specified as 24 knots.
I have no more knowledge than you, or anyone else, about exactly what we'll get, but I'm not going to assume that it's what the RFI says is the minimum requirement, across the board.
The drawing published by the MoD specifies under 'Adaptable' (i.e.what the ship should be capable of taking) 'Medium range gun >76mm capable of Naval Gunfire Support'. Given the available naval guns, I think it's safe to assume that '>76mm' means 127mm. 'Adaptable' is additional to the 'Core' required for the RN, but the ship must be capable of taking it.
The proof is in the pudding, I am sure smaller navies will be watching this one closely.
76mm is a capable round. But going all 5" is a better bet, particularly for the RN.