Depends on how they handle it.
Simply announcing Shenmue 4 but without revealing too much, like a simple 1 minute teaser with the in-game engine (or CGI even), and then say "more news soon", without giving a time frame for those news might attract people to look closely at them and what they have to say and show... So attracting indirectly people into looking at Wanted Dead.
Also, it might be good for their momentum to have a game that attracts people towards them as soon as the other one releases.
I believe that if they announce Shenmue 4 now, they will simply announce the game and won't reveal much more.