It took full time work for years and dozens of iterations of foil designs, foil management, crewing and sail management techniques and power management before they got the AC50s to foil all the way around a race course, and that was with a much lighter, more maneuverable platform. I understand Oracle had a team of dozens of people who were daily working on the incremental pieces that got to consistent foiling.I think their aim would be to foil for 100 % of the race.... however, even at sub foiling speeds, the foils generate a lot of lift, negative lift on the upwind foil would help in this scenario.
Now ETNZ are asking teams to try to reinvent that process on a larger, heavier,more expensive platform with a theoretical foil design that has never been raced before.
Good luck with that. I would guess that wallets are slamming shut all over, with a wait and see attitude before a few of them open up for next time.
My 2 cents.