I would love to see some kind of "native" integration with the popular Phaser 3 game engine. http://phaser.io/
Perhaps the GameSparks JS client SDK already enables support, but the ideal case would be either a template + tutorial to get it running with GameSparks or a separate SDK for "painless" integration.
If you have not anticipated the upcoming rise of Facebook Instant Games (built on HTML5), that could be a big strategic oversight. :) Phaser support would strongly signal to the wave of developers jumping onto that bandwagon that your service would be a great fit for their games.
Apologies for the delayed response. I'll log this as an SDK feature request for you.
Also, description about Facebook platform itself is available on https://developers.facebook.com/docs/games/instant-games/guides/bots-and-server-communication#backend (probably access to open beta is required if link deosn't work).