As for Sega showcasing it, technically, they still own the property and they loaned it to Suzuki. Suzuki admitted a long time ago that Sega would give him the license if he came up with the money himself. Does this mean Sega is officially back to promote Shenmue? Are they part of its Japanese release? I guess time can only tell.
Sega and Koch Media (Deep Silver) are publishing and distribution partners for a long time.
Koch Media is the distributor for pretty much every retail Sega game in Europe,
thats why at events like Gamescom Sega games are always in the hall of Koch Media. there is no Sega hall,
Sega is always in the Koch Media hall.
So it makes sense that Sega is helping out Koch Media now at a japanese event
because besides Shenmue 3 Koch Media doesnt have any own japanese games
and Shenmue 3 is a part of Sega and Koch Media.
So why send two companies?
I think for now this has absolutely nothing to do with a special Sega promotion
or Sega as a publisher or Sega being back for Shenmue 4. Sega is helping out
because it wouldnt make any sense to send Deep Silver for just one game
when the IP owner is japanese and a official partner. All of this coming stuff, what Sega or Sony will show,
is still arranged with Koch Media.