And exactly because it's a "wannabe" Shenmue is why I think Sony wouldn't fork whatever much money Shenmue 3 would cost. They already have a similar game in their catalog, which pretty much is only really popular in japan (so far). Shenmue would be a huge, huge risk, and could take sales away from Yakuza (or vice versa). Publishers tend to look at their games as a catalog and check variety, I think Yakuza is "PS3's Shenmue", so imo it would be even riskier.
MS on that matter... they don't have Yakuza, Shenmue II was on the Xbox, and they are looking to boost their presence in japan, so there is something there.