Honestly, that's a good question.
My personal opinion would be until Microsoft drops releasing 32-bit Windows releases and updates (and all Windows OSes that are still supported by Microsoft; Windows 8.1 and Windows 10 whichever build number is the last with a 32-bit release), and only releases/updates 64-bit builds. Don't think it'll happen for at least another few years. Maybe 5? Maybe 10? Could be 20 for all we know. Don't think it'll go away anytime soon though.
Fortunately Windows is not like macOS, where Apple has dropped all support for 32-bit apps in Catalina even though I wouldn't be opposed to Microsoft doing this in a slow and steady depreciation process allowing users and developers to adapt.