What will after xA / xB model year? After 4 years later, what might come in to U.S. ?
These are wild guess what Toyota will bring up to Scion. ( all with same engine 1NZ-FE )
FunCargo
http://www.toyota.co.jp/Showroom/All_toyota_lineup/funcargo/exterior/images/ex01_svg.jpg
WiLL CYPHA
http://www.toyota.co.jp/Showroom/All_toyota_lineup/willcypha/exterior/images/ex01_svg.jpg
RAUM
[img]http://www.toyota.co.jp/Showroom/All_toyota_lineup/raum/exterior/images/ex02_svg.jpg
ALLEX
http://www.toyota.co.jp/netz/lineup/allex/exterior/images/ex01_vga.jpg
Porte
http://www.toyota.co.jp/Showroom/All_toyota_lineup/porte/exterior/images/ex03_vga.jpg
Passo
http://www.toyota.co.jp/Showroom/All_toyota_lineup/passo/exterior/images/ex03_vga.jpg
see all funture-model-to-be @ http://www.toyota.co.jp/Showroom/carlineup/index.html

All good guesses. Its to hard to say if any of these will be the next Scion. The main reason is like you said, If the xA & xB are still around for another 2-4 years, Toyota Japan might just get some news cars that could become the next Scion. I my self would love to see the Will Cypha come to America, that thing looks sweet. Also there has been a topic like this before. http://www.scionlife.com/forums/viewtopic.php?t=9018&highlight=future http://www.scionlife.com/forums/viewtopic.php?t=18666&highlight=cypha