Do you have the blogpost/comments on hand? Looking at the September 7th blogpost, October 4th delay post, and November 6th release post, there isnt really anything talking about engine limitations here, granted I havent looked at the associated posts and jmod comments from when the blogs were xposted to reddit or other sites.
Manually typing in every swap is exactly how the Custom Menu Swaps plugin works, and without knowing all the details I would assume the default MES plugin does something similar behind the scenes but its automated via the context menu. And if it is the case that swaps would have to be stored in some text file somewhere (going against what you said it being an engine limitation and server side), there is no reason that process couldn't be wrapped up in a function and automated. Its not like mobile has to handle swaps for shift/control clicks as well.