Even Win 7 Upgrade for FREE may not be enough incentive
A free upgrade from Win 7 would certainly help, although that may still not be enough. Most of the XP reluctance to upgrade has more to do with the organizational or embedded design costs of validating the systems and all the other software that had to be migrated than the OS cost.
A couple of other issues. 1) Hard to think that the Microsoft Board of Directors and shareholders would be OK with leaving a lot of money on the table, either. 2) Given the trend to consume more compute cycles with every iteration of Windows, the Win 7 HW may not be able to run Threshold. For example, 2-point touch from the 2010 era, although compatible with Win 8/8.1 is pretty clunky. No universal TPM from that era really needs a solution even if it's a USB dongle they brand and sell separately. Will my 2010 Dell Duo 1090 with 2-point touch and single-core Atom really work with Threshold? Would Microsoft even want crippled instances of legacy HW trying bravely to run Threshold even out there?
Finally, I was really happy with how Microsoft rolled out Win 8. They still need to fix the basic Windows touch so that you can reliably do such simple things as close windows and start text entry with your finger -- THE FIRST TIME. (HINT: make the icons bigger, or at least give me a choice to in Control Panel.) They need to do as great a job as they did with the Upgrade Evaluation Tool. And having the $30 upgrade like they did from Win 7 to Win 8 Pro for the 1st 3 months is a good idea to repeat; maybe this time without the sour taste of dropping Windows Media Center.