Here's my two cents:
Starts with 12 teams and goes for 13 legs* (I like the 12 team seasons, and I feel they should bring the leg count back to 13).
Note: I personally count double-length legs as two separate legs, but denote them as one. (So, even though it may say 12 legs, it's actually 13, since one leg was twice as long).
Leg 1: New York City, U.S.A. to Buenos Aires, Argentina (EL- 11 teams remain) New York deserves to have a starting line, especially since it's season 20. A good time to do a throw-back to the original. Buenos Aires is also a good city that hasn't been visited since Season 7, and could easily field another leg.
Leg 2: Buenos Aires to North-West Argentina (EL- 10 teams remain) Central and Southern Argentina have been used a lot. Would be nice to utilize this area, as well. Also, a good time to do a Switchback of the meat eating Roadblock from Season 7. It also, helps us transition to our next location.
Leg 3: Salta, Argentina to Asuncion, Paraguay (EL- 9 teams remain/U-turn #1) New location, with several possibilities in terms of tasks. Throw in a U-turn here to maybe spice things up a little.
Leg 4: Paraguay to Rome, Italy to Vatican City (NEL- 9 teams remain) Rome definitely deserves another visit, especially since it hasn't been used since Season 1, and on top of that, was only used in a couple "find the monument" tasks on that season. Also, an actual stop in the Holy See would be nice. Even a pitstop would suffice.
Leg 5: Rome to Pompeii/Naples/Capri, Italy (EL- 8 teams remain) I love to see the Mediterranean coast. And this leg would feature it prominently. Have clues and tasks throughout the region, and maybe end on the Isle of Capri.
Leg 6: Naples, Italy to Riga, Latvia (EL-7 teams remain) I'm actually quite surprised Latvia has yet to be used. Most likely similar to the Lithuanian (S12), and Estonian (S15) from before. Also, could be considered the "cold leg" of the season, since it would be winter up there.
Leg 7a: Riga, Latvia to Nairobi, Kenya (DL- 7 teams remain) This will be a double-length leg, or super leg as some call it. Have the majority of this half of the leg in and around Nairobi with the midpoint within the city.
Leg 7b: Kenya (EL- 6 teams remain) Move from the city onto a national park or game preserve. Have a task or two based off of the animals native to the region.
Leg 8: Nairobi, Kenya to Male, Maldives (EL- 5 teams remain) I feel there needs to be at least one tropical location per season, and this country would be a perfect fit for just that.
Leg 9: Male, Maldives to Christchurch, New Zealand (EL- 4 teams remain/U-turn #2) Love seeing the green hills of New Zealand, and think that they would look wonderful in HD. Also, they haven't been to the Southern Island in a while.
Leg 10: Christchurch, New Zealand to Chengdu, China (NEL- 4 teams remain) I feel this city is a must see in China, and a little (not very) surprised it hasn't been visited quite yet. Many food and cultural tasks can be done here.
Leg 11: Sichuan, China (EL- 3 remain) Not necessarily staying just to Chengdu, but traveling around the region. Again, plenty of tasks that could be used for this area.
Leg 12: Chengdu, China to Vancouver, Canada to Seattle, U.S.A. (Finale) I believe Vancouver could be a wonderful intermediate location. Have a couple of tasks in the downtown area before taking the ferry from Victoria across to Seattle. Have one or two more tasks in Seattle (final memory challenge please).
11 countries (including U.S.A.): 3 of which are completely new (Paraguay, Latvia, the Maldives), 2 with actual visits for the first time (Vatican City and Kenya), 3 more that haven't been visited in several to many seasons (Italy, New Zealand, Canada), and the last two visiting new regions within the country (Salta, Argentina and Sichuan, China).