Shenmue 3 is coming out for sure. There's no offical announcement but Shin Ishikawa of AMD2 said the series continues because of fan requests and that we should look forward for new games on the Xbox. I would buy a Xbox for Shenmue 3 because that is how much of a Shenmue junkie that I am.
There are even screens:
Screen numero uno
Dos
Y Tres
The series probably wont stop with shenmue 3 because Shin Ishikawa drew out a story timeline that suggests that the series will surpass only 3 games.
This guy has awful handwriting.
And just for some interesting info, on Shenmue 2 for xbox, you can find some loading screens for locations not even in the game. They possibly took out a chapter that they didnt include in Shenmue 2x for whatever reason.