Adam: I'll try to respond to some of your ideas with examples I know of.
I think I started a thread when I first joined this site called "Double-Ended Holes" and got no response... (Mike Keiser actually suggested that we build a green near the 13th tee at Pacific Dunes so that hole would be double-ended. I thought it might be distracting feature to have on the most spectacular natural hole on the golf course, but it was the start of conceptualizing The Sheep Ranch.)
I think one could work a 'loop' of three or four holes in where they return to the same general location so that they could be built as double-enders. (By 'loop' I mean a few holes like 8, 9 and 10 on Bandon Trails - just looking at the routing, you could make those three double-enders and basically add three holes to the same corridor). I think there are some really interesting possibilities there. And I imagine that it would be especially fun/challenging to design them well.
I believe Tom McBroom did a bunkerless course called Hockley Valley - it had some good holes - I seem to remember it as being bunkerless - but maybe not... (I think you're right on that one. The best bunkerless course by far is Royal Ashdown Forest in England, where the "royal forest" designation prohibits man-made features, including sand bunkers. Mostly, though, bunkerless courses are low-end places which can't afford them.)
I have done sketches for a par three made up of only perfect circles Green, tees, bunkers, etc) which I think could work quite well and look quite beautiful (but cerainly not natural). (Certainly not!)
What about using a section of beach which can be carried, but if it isn't (and the tide is low enough) the sand can be played out of again - (This is the first hole at Machrihanish, see the "favorite first holes" thread for a picture.)
I'm also interested in situations where you really can't go directly at the green at all - you have to use the ground around it to hold it. (I agree that this is cool and very rarely done. The 12th at White Bear Yacht Club is one of the best I've seen at this ... the green falls too hard away from you, so you have to bank in the approach off a shoulder at either side.)
This thread started with Tom Paul's idea of a hole which was simply a huge open expanse along a ridge - whose fairway might be extremely wide - with no bunkers or hazards at all - just an immense, open expanse of natural terrain with nothing in particular to aim at - and nothing in particular to avoid. Yet I imagine that this would only be a first impression - there would be subtlties which revealed themselves as you played the hole - better places to be, better angles to hold the green from, worse places to miss - but nothing would jump up and bark at you. You'd have to search it out yourself, and think. This type of hole, if used just once on a course, might be very intersesting. (That's a tough one for me. Most architects would prefer to identify one or two favorable routes and accent them, instead of not making a decision on their own. I don't think you could do this for one hole without it being panned ... you'd have to do the entire course that way, as I was talking about on the map I'm looking at now.)
Philippe: Par is only in your mind. If you can keep it way in back, you can design everything you talked about. Just be prepared for some people to look at the scorecard and complain, without even having seen the golf holes!