Suppose, hypothetically, that you are a vendor and you want to push people to upgrade more frequently. No problem, you say, you will just reduce the support period for your old releases. This is a magic trick that will surely cause everyone to upgrade at least as fast as you want them to, basically at a pace that you chose, right?

Well, no, obviously not. There are clearly at least two forces operating here. On the one hand you have people's terror of lack of support; this pushes them to upgrade. On the other hand, you have people's 'terror' of the work and risk involved in upgrades; this pushes them to not upgrade. Pushing on ever shortening support from the vendor side can only get you so far because the other force is pushing back against you, and after a certain point people simply don't move any more. Once you've hit that point you can reduce your support period all you want but it won't have any effect.

Generally I think there will be diminishing returns from shorter and shorter support periods as you push more and more people to their limit of terror and they say 'well, to hell with it then'. I also suspect that this neither a linear decay nor a smooth one; there are probably inflection points where a whole lot of people will drop out at once.

Aggressively lowering your support periods will have one effect, though: you can persuade people to totally abandon your system and go find another one that isn't trying to drag them around through terror. This is a win only if you don't want users.

(By the way, the rapidly upgrading products in the real world that do this at scale don't do it by having short support periods.)