The way I see it this is good news. Like a few have already mentioned this isn't a move to replace James, on the contrary this seems like he's beeing brought in to play alongside James on the right.
We've been longing for elite rotation for years now, especially on the right and finally the club are backing our coach. This is akin to when Conte wanted Alex Sandro alongside Marco Alonso we would have two elite options for wingback.
With Cesar getting older I see James getting more play at RCB this means we need another exceptional athlete to play RWB for us. Hakimi is proven in both the Bundesliga and Serie A. He's played under Conte and won the league and if Tuchel wants him I'm all for it. Long term for £50m I think this is a good deal for us.
Of the three positions mentioned Tuchel wants signings I believe they are midfield, right wing back and striker. It's nice to see we're already making a move so early on rather than waiting til the end. If the club has learned anything from last summer, it's get your targets early and let them integrate into the squad.
Having James, Cesar and Hakimi covering our right side for the mid term to long term (until Cesar leaves) sounds good to me. Also it gives us a clue as to what shape we'll most likely see next season, highly likely 3atb remains a common feature if not every game expect to see it fairly frequently.