I agree, it is tough on a formula fleet if one design becomes the Olympic boat... makes you wonder if the Olympics is worth it...
That said, my half thought out idea for dealing with an F18 as an Olympic boat is similar to Timbo's with taking the Alter cup model.
Basically say "F18 is the Olympic class Multi". For three years leading up to the Olympics, don't pick any specific model. One year before the Olympics have a competition from the manufacturers, select one to be the Olympic Boat. The manufacturer then HAS to lock the design down at that point, and supply new boats at the Olympics for each team (and brand new identical sails / foils / etc, exactly what the laser class does).
Advantages, no picked boat for most of the cycle, lets all the manufacturers develop their boats / models, top teams with funding will buy what they want / can, lost of used good boats on the market. Yes, could drive cost up for olympic teams, but does not need to, as the F18 fleet is solid enough you don't HAVE to have the top boat to win.
For the qualifying year, everyone is on the same "olympic" boat, no need for an arms race in equipment, truly comes down to the sailors. Yes, the chosen boat (company) has an advantage, but for all the hundreds of sailors who aren't going to the olympics, all the olympic teams will be selling off their older boats and we can all just keep sailing whatever boat we like.
After the Olympics, go through the same cycle as before, allowing other manufacturers a chance to get the Olympic bid again.
I know, lots of problems, but if we have to have an Olympic Multi Hull that is mixed, the F18 makes the most sense as a design. So we have to come up with solutions to make sure that doesn't kill one of the best fleets (IMO) going at the moment. So some variation of a bidding process that both selects a specific boat for the olympics without killing off all the other designs at the same time needs to be found. I think my idea is a good starting point. How a company would bid, the exact "open" time versus "just one boat time" should coincide with Olympic qualifying times, etc etc.