The Forma and all reading apps I've used on Android say they support Epub 3, including Moon+ paid, Google Play Books, and FBreader free. FBreader says on the Google play store they support "(including main features of ePub3)." So my device and app support should not be a problem.

I am already using the kepub format on my Forma and using Calibre to send that format to the Forma device specifically (I actually started the thread you linked to).

But I'm asking specifically if it's worth converting your epub format books in Calibre from Epub 2 to Epub 3 (independent of the process of sending .kepub format to Kobo devices, which Calibre does automatically when you have epub files in your library). Basically, I'm wondering if it's worth the trouble to convert all my epub source files to Epub 3, and if so, what feature differences would I see on current devices that say they would support it? It sounds like you're saying, not much.