I completely disagree on the dynamic icons. When I want to play some music, I know I'm looking for a two-eighth-note icon on a pink-orange background, and I don't want that background to change to black cause I listened to Dark Side last.
I don't want 'photos' to show me the latest photo I took as that could have been days ago and now finding the photos app is really difficult.
But if just part of the icon changed to indicate something, like your stock folio position (without the red/green background idea) then it works both ways. The icon always looks generally the same - it's a graph - but it changes to indicate some data point that may save opening the app.
That said, how would the icons update if you don't open the app. Each app's developer would either have to send out an icon update notification or would have to provide some level of running the app on a regular basis to regenerate the icon.