When they went back to Australia in 2005 they also had problem selling the gigs, I remember they had to do promotion because it wasn't selling as expected, I even remember Guy telling on his site about one gig in a theatre in Sydney that wasn't selling well and that was a very big chance of seeing them in a more intimate scenario...
If they did a last DS tour, there would be hugh demand so they should do something to control it, not going out of the smaller size they would want it to be, and usually big names like The Police or Genesis, even Clapton nowadays, what they do is offer a premium account where you pay a certain amount and you have access to priority tickets before it went on sale for general public. I don't like this way as scalpers can register and buy tickets as those premiums accounts are open to everyone, but that's the easy way for them to organize it.
I would prefer that from MK site they use another system like, giving that priority to users registered before the last tour went on sale, or that bought tickets for any of the previous tours, and after that, a second presale for premium new users, and after that, general sale. I truly think that if there is a last DS tour, the old loyal fans should have priority to the ones that are only interested in a last reunion. Yes, judge the loyalty can be subjective, but the being registered before the last tour could be something maybe better that if you never bought a ticket to any of the MK tours, but I think that MK had toured alone enough so you have might seen him in one tour or the other....
Anyway, this is very unlikely to happen. Maybe release unreleased stuff is something that might happen if John is on charge and MK has to do nothing except saying "Ok, go on", because if MK is on charge... just forget about it.