I priced out a few itins and basically the 90% premium is right on. Curiously, they are marketing the exit row access as through the 'Flex' fares as well, so you effectively have two different price points for some of the new Premium seats. That seems messy. For some of the itins I looked at, where the lowest fares were sold out anyhow, you now get more than you would have under the old system as you book into Flex or Premium, so that's a plus.
Overall, it seems like a mistake to bundle the fare classes together with the premium seats rather than to up sell the premium seats as an add-on. That way they'd have the option to load more high fares if demand is good without tying them to the number of premium seats available. I'm sure they'll make adjustments if sales don't go as planned. They'll know pretty quickly if no one buys the premium fares until the econ and flex are sold out that it isn't the product itself that is driving sales.