My western-US trip was amazing, and while another New England winter lingers interminably into spring, I'm thinking about where to go next. The answer (for a depressing reason I'll mention later) is: Australia and New Zealand!
This trip will be on the order of 6-8 weeks, rather than 6 months, so it's a different scale of planning, but the distances involved more than make up for it. What I'm thinking now is to rent a camper or sleeper van and drive around the circumference of the continent, either all the way or in a large backward C, skipping the vast and unpopulated west coast from Perth to Darwin. I'll make stops in major cities and at several national parks for a few days at a time. It will probably be around this time next year--March--making it late summer/early fall in the Southern Hemisphere.
Luckily, I'm not the first person to have this idea, and there's a whole camper-rental industry that caters to weirdos who want to drive long distances in and around Australia (including one that rents graffiti-ed molester vans). There will be altogether less camping and backpacking involved in this trip, but I do plan on sleeping in the van, camping, and doing lots of hiking, swimming, and wandering around. I'd like to drive into the outback enough to say I saw it, but I don't think I want to spend much time there. Uluru (Ayer's Rock) is probably too out-of-the-way.
And New Zealand! So far, I haven't thought much about it, but I know I'd like to see it. Depending on the amount of time I want to be gone, I may not get to spend much there, which could be too bad. But at this point, things are still very up in the air. I'm only starting to make dents in the Internet research. Next will be the library. Check for infrequent updates.
Oh, and the depressing reason? Skip if you don't want to be depressed. Scientists estimate that the Great Barrier Reef will die off before the end of this century, and possibly within 50 years. So, yeah. While it lasts.