Google Chrome to block Flash toward end of 2016
According to this story, Google Chrome is going to start disabling Flash content by default by the end of the year:
"Under its current vision, nearly every website would have Flash content blocked by default. Visitors would still be able to enable Flash content on a site-by-site basis, but they would have to specifically choose to do so. Chrome would display a prompt offering to enable Flash; if chosen, Chrome would remember to run Flash on that site for all future visits."
I think this is a very significant factor in the choice of whether or not to include HTML 5 output when publishing. (in other words, I'd say always check that box)