I could see them doing a leg in southern Africa. Maybe not South Africa specifically, but since it's only the northern countries that are affected at the moment it's very plausible South Africa or Namibia or Malawi or something could turn up.
If they do go to South America, I'd hope for Paraguay (the only non-Caribbean-bordering country still yet to appear), but with Brazil in TAR18 I think Argentina's most likely.
Europe? Hmmm. PIIGS are out since the governments won't spend money bringing the show to them, and we've seen most of the remaining western Europe countries in the past four seasons (by my count only Belgium, Denmark, and the micronations are left), so I'd expect an eastern European country, if any. Probably a new one, since no eastern European countries have been repeated yet (assuming you count Austria as "western"), and hopefully a Balkan state. Serbia's plausible, as is Albania, or maybe even Bulgaria.
Asia's harder. Since Family Edition, either China or Japan has been done in every race except 13, but 18 was the first to have them both, so maybe we might skip them this time? But it's hard to find any regions they haven't hit recently. Kazakhstan was apparently a real pain the first time, so I don't think we're going back or to any other country nearby (all with even worse infrastructure, and some not safe for women in particular). The Middle East is especially Not Safe Right Now, and we've done India and the neighbouring countries twice in the past two seasons, so they're most likely out. South-East Asia's a mainstay, but aside from three new countries (Indonesia, Laos, and Brunei), they've all been done in the past 5 seasons.
In summary, I suspect we'll get about 8 or 9 countries, probably containing at least one Central/South American country (probably Argentina and one other); South Africa (and possibly a country nearby); at least one country that was part of Yugoslavia; at least one of Thailand/Indonesia/Laos/Philippines, probably two; and a North American country.