Let's get a few things straight:
First, Intent on not moving the boats between coasts and the reality of what could happen in the next 30 years are two different things. You can't plan your acquisition of assets on your current intent without considering potential future events. Therefore, I don't think it adds any plausibility to a mixed fleet option.
Second, based on the interview given by RAdm Robinson above we have to consider the fact that numbers of boats of each type and per coast would have to play differently in such a scenario. When I was in, we needed three boats to keep one in operation at all time. I recall only a small window where that was not the case while the O-boats underwent the SOUP refits. Robinson, however, mentions the need for a ratio of four boats to keep one operational. I don't know if this is based on actual lack of capability to do more (and go to a 3 to 1 ratio) for technical reasons as the boats are now more complex and sophisticated, or if it is simply because, under the current availability of trained personnel and the fleet of four boats the RCN has gotten comfortable with that ratio. In any events: Robinson indicates the RCN requirement as being a minimum of 8 boats, so one per coast is available, and preferred 12 boats so three are available, including one deployed to the Arctic. In this last case (12 boats) with three boats deployable, including one to the Arctic, each group of four would have to be colocated, so one coast (likely the East coast, which has better and more direct access to the Arctic) would have to have 8 boats, to the other coast's four.
In a split fleet, would the RCN want to wait as long as it would take to get 8 boats from TKMS, on one hand, or to have a secondary fleet of four boats of a different model.
P.S., I don't think that even a split of 6/6 boats between Hanwa and TKMS gets us to 12 boats delivered to us as fast as a single order for 12 with Hanwa alone.
