2 million seems a bit unrealistic.
that would be more copies than the Resident Evil HD Remake on PC/PS4/Xbox One
which sold about 1+ mil copies and Capcom saw that as a huge success.
the Final Fantasy X HD Remaster on PC and PS4 didnt sell 2 mil copies,
Last of Us Remastered on PS4 didnt sell 2 mil copies,
Yakuza 6 had the best NA start/release of all Yakuza games - they sold around 1 mil copies worldwide.
the only re release (Remake, Remaster) that reached more than 2 mil copies, was the Crash Bandicoot N Sane Trilogy on PS4.
so 2 mil copies for Shenmue HD seems totally unlikely if you compare it to other re releases.
doesnt matter if they are multi platform or not. so lets not overact with the numbers
or we might end up pretty disappointed.