I doubt it's large enough to make Shenmue 3 a viable financial risk.
The reason that Shenmue failed to turn a profit for Sega had nothing to do with it's budget and everything to do with the limitations of the Dreamcast.
Shenmue sold over 1.2m copies on a console which sold little over 10m units. That equates to more than 10% of Dreamcast owners purchasing the game. Had the game been released on a more successful consoles it could have potentially broken records.
Let's say, for example, that Shenmue had been a launch title on the PS2 instead of a Dreamcast game. The PS2 sold over 155m units over it's lifespan and so taking our 12% sales per console figure we're looking at around 18.6m copies sold - which would have beaten GTA San Andreas' 17.33m sales and made it the best selling game on the PS2 (Considering GTA SA was the sixth game in a hugely successful franchise - that's pretty damn impressive for an new ip). Add in the fact that the better launch games tend to get a boost in sales due to the limited variety available at launch as well as the exponential growth in sales through word of mouth - and Shenmue could have easily sold 20m+ units on PS2.
Had it not been released on a dying/dead console (or not released at all in the case of the US) I've no doubt Shenmue 2 would have outsold the original due to several areas being drastically improved (the GTA series has shown a steady increase in sales per release as gameplay has improved) and so it's entirely possible that the games would have clocked in 45m+ sales which would have equated to about $1 development and marketing costs per copy sold and in turn - HUGE profits.
Of course this is all hypothetical and there are plenty of arguments to be made and flaws in my logic - but I'm positive that had it been available to a wider audience rather than just Dreamcast owners - Shenmue would have been a commercial success (at least 18m copies between the two games). Given the capability of modern consoles, the drive and passion of Yu Suziki and the innovative nature of the series - a reboot would be hugely successful (unless it's on the Wii U, of course).