Pat:
Combining the 9th and 18th into one enormous melded fairway or something slightly similar might not work at all for a whole host of reasons. The only way to tell would be to go out and look at everything that's out there topographically and otherwise.
On the other hand, maybe it could work to create a ton more interest in some way. The tees and the positions of them would have to be carefully looked at too to determine whatall drives could do optionally coming off those tees to areas other than their present fairways with the ultimate destination being the opposite greens!
There's certainly no harm in looking and if it turned out somehow that from either tees there was something interesting or reasonable that could be created to induce players to go over to the other side off the tees or even into the middle between the holes then so much the better.
But you're right you don't want to create a situation where one hole would play much easier this way and the other harder or any combination of that.
The interesting thing to me would be if this really could work somehow to create some really interesting and useable additional options that varied greatly, then what's wrong with that?
The idea to me with multiple options on golf holes, particularly very varied options is if all or most of those varied options come into some state of equilibrium somehow by players such as touring pros then basically you've created some ideal situations and some fascinating multiple strategies.
But the point is those varied options have to be readily used and in some degree of balance to make something like this functional, useable and additionally interesting. If you created a situation on those holes where almost ALL the pros ended up playing both holes in a different direction and in a different way than either of them are played now then what you've probably accomplished is not much more than making both holes easier and maybe even more one dimensional---and that of course is not the desired goal. But making them far more muliti-optional than they are now might be provided all those options and strategies are used to some degree of balance!
Who knows--but it's worth a look. Wayne has a point too that melding together all this might look odd--but maybe it all wouldn't have to be melded to create this same basic affect. It's worth a look if for nothing more than the fun of looking.
Also, just imagine how differing winds might work to create additional interest in a set up like this if it was reasonable!