By the time the T26 will be in service they will be citizens (I don't know your citizenship rules, for us is 20years of residence).
For Australia its more like 4 years if that is what you want to do. Eligible visa, 4 years (mostly in Australia, some holiday trips etc allowed)you can apply for citizenship. Australia is a major migrant destination. We usually have around 250,000 skill migrants migrating to Australia.
For ADF military transfers, 5 years in a compatible force, and currently serving and less than 48 years old.
However, and as previously discussed, the F100 is not only mature as a design, but is over aged. Any new build might look like a Hobart, and will certainly have the limitations of a Hobart hull, but its equipment fit will be very different due to the unavailability of equipment which, for the originals, was ordered 15 years ago, and at what was effectively the end of the production life of some of them.
Does sea4000p6 involve the replacement of these older systems? Supporting material capability of the hobarts (CN40)? I recall reading that electrical distribution, data, mechanical services, generation would be looked at as part of the upgrades. Possibly why the upgrade at $5+ billion is so expensive (?).
The design was significantly updated for the American ffg(X) bid. From ladders, access hatch sizes, corridors, damage control, power generation, growth margins, stability, power distribution, stores, fuel bunkerage, weapon handling and storage, length etc. I've heard the changes are more significant that between Burke Flight II and flight III.
Any new builds I assume (again no details from anywhere) would be of this type. The revisions made it a much, much better ship. With out of the box Aegis 9 or 10, Spy 6, latest engines, latest subsystems. Very different ship to HMAS Hobart hitting the water in 2015. That probably undermines the idea that they are the same proven class of ship, but I guess that is more likely what would happen.
The time between Cristal Colon hitting the water and Hobart was 5 years.
The time between the existing Hobart and any Flight II Hobart's hitting the water(2029?) would be similar to the time difference between Hobart and the original Alvaro de Bazan (~15 years).
Even if the Hobart was a complete new design and new everything. After ~15-20 years it would have aged out as well.
We could have updated Hobart. We chose not to. Batch buying and delays made this decision silly.. Now we are spending $5billion.