If that was to be the possible case would we be better off getting 3 more AEGIS/AN-SPY1D vessels or getting them with the Saab 9LV/CEAFAR 2?
I think the only real mix is AEGIS/CEAFAR or 9LV/CEAFAR. With future munitions, SPY1D having a limited future in new builds (upgrades?) I would say CEAFAR is the way to go. Its likely to be mounted higher than SPY1D can be.
9LV verse AEGIS. Others know more about that. But I would assume AEGIS is going to be preferred if firing SM-3 (I would imagine integration is easier/cheaper/faster with AEGIS), tighter integration with the US fleets or acting more like AWD's in an air defence role rather than a GP frigate. The downside is trying to keep step with the US on upgrades. Either way, both are capable and workable.
Personally I would probably like to see 3 x F-105 basically dual hanger/Ceafar AWD with AEGIS. This would give 6 top of the line Air Defense ships. We can then manage AEGIS updates, Sm-3 etc. Really it would be Flight I Hobarts and Flight II Hobarts. I would like to see Sm-6/Sm-3 integrated on all of these and an AEGIS baseline that supports SM-3 BMD from the get go.
I would then push the UK to make the 2nd batch of Type 26's (Australia's first batch) the longest possible hull form with the most amount of displacement. Ensuring 48 strike length VLS in the hull (none of this 24 strike only bs, but I would keep the 24 defensive VLS for quad packed ESSM and nulka). Two x 35mm millennium mounts and two phalanx mounts. 9VL and CEAFAR. I think that would be a strong combination.
I think that would be a good mix. With two main common type of hulls, with different focuses. I think they would compliment each other nicely.
Hopefully the UK and Canada build a useful number of Type 26's. Sharing upgrades and development, training and superior inter-operation.