We created the Add-ons Marketplace to provide functionality that isn't part of the core PlayFab service, pre-integrated wherever possible (to save on development time and SDK fatigue, as well as take care of any updates of those services that can be accounted for in our integration code), and at a negotiated price so that you never pay more for them than you would if you went to those companies directly (and did all that work yourself).
Originally, we had a number of possible future integrations listed in the main Marketplace pages, in order to prompt developers to give us feedback on which ones were most valuable to them via the "notify me when this is available" option. What we found though, was that those listings were causing confusion, so we've removed them from the Marketplace itself to make sure we're clear on what's available.
So what does this mean? Well, first and foremost, don't worry - all the information we've collected to date from developers is still part of our tracking, so if you clicked the "notify me" option on one of those integrations, we still have your info and we know you were asking about it. But we're also adding those integrations to this, our Add-on Marketplace forum, so that developers can Like them there, to help with prioritization.
And, of course, if there are other integrations you'd like to see, please feel free to let us know by adding it to the forums. The more information we have on the needs of our developer community, the better able we are to prioritize our work.