Have you tried Kweb yet? I'm delving into it now for the very same reason. I've been searching for digital display/kiosk solutions that will allow me to play a video in a window of an html page. I need live web content for the rest of the page, but the video can be a local stream.
Streaming a YouTube playlist in an iframe works (mostly), but depending on the browser (and I have tried many) it will either cause the pi to overheat, or it simply displays poorly. Kweb says it has the ability to run omxplayer in an iframe. From there you can stream a local playlist. Stand-alone, omxplayer has had the smoothest playback for me on the Rpi3 (as you probabably already know). So if I can get it in the iframe of an html page, I think that might be the answer.
Maybe that's your solution too? I'll post an update if I can get it working properly. Otherwise, maybe Screenly is a solution that could work for you?