I would much prefer for Kongregate to develop and publish their own C2 plugin, since there are hundreds of third-party services out there, it's a constant burden trying to maintain them, and it's not our API/service (they obviously know their own platform better). Our plugin was developed a few years ago when we were just trying to get off the ground and offer some extra options to developers. I'd encourage you to go to Kongregate about further support.
1. Kong is by far the biggest and most profitable one of them all.
2. They might know their platform but do not know you.
3. Kongregate is a moloch of portal. Asking them to make the plug is like telling Microsoft it is THEY who should adjust to YOU.
4. out of those "hundreds" - there are only 3 that matters in case of browser games: Kongregate, Newgrounds and Gamejolt. In that order. Kongregate plugin was made by you, Newgrounds was made but never finished by a user who never comes here anymore, Gamejolt plug was made by GJ staff and is mostly maintained by them.
5. You do not have to re-invent the wheel. Just add the Video API to already existing plugin.
6. Burden or not - it is part of the deal. The most native platform for C2-made games are browsers, and you cannot develop games to browsers without trying your luck on Kongregate.