While the focus is rightly on video, there are a huge number of games written in flash. In the short term this s probably a hug boost for unity... But as flash dies there will be a lot of games that die with it.
(FWIW here's where Adobe Captivate is with HTML5 support: https://helpx.adobe.com/captivate/using/publish-projects-htm...)
Though I don't disagree at all, transitioning from one proprietary, single-vendor, closed-source plugin to another isn't actually going to solve the problems that killing Flash is supposed to solve (apart from the one where Flash is also a gigantic legacy-code monument to all our sins, of course ;) ).
From what I remember it's not as performant or reliable as the plugin, so there's some work to be done on unity's end. Beyond that, if browser makers want to replace native code plugins they have to give a better alternative. WebAssembly might help, but since it's essentially running in the same vm as JS I'm not sure it'll be faster other than the parsing overhead.
... two things that absolutely kill videogames, so it's more accurate to say "Unity you will output WebGl-based games" (at some indeterminate point in the future).
Agreed that it's a step in the right direction over alternatives though.