Plex's integration in Universal Search will require significant design changes to Apple's implementation of Universal Search.
Currently there are zero custom content databases in Universal Search.
How it works currently:
- Third party content provider uploads their content library list (for each region) to Apple's servers
- AppleTV records the voice query and sends it up to the Apple cloud
- Apple cloud translates queries
- Apple cloud performs search against all content libraries in region that user has access to
- Apple cloud returns the results to AppleTV.
For that design architecture to work with custom libraries, you're going to have to upload your entire Plex content to Apple's cloud servers. Unlikely that's ever going to happen for a whole host of reasons (and would still require some design changes).
No, for custom libraries to be searchable in AppleTV's Universal Search, the following change would have to happen:
- AppleTV designs and implements a new feature: Local Universal Search
- Third party content provider registers the local custom library with AppleTV's new Local Universal Search API
- AppleTV records the voice query and sends it up to the Apple cloud
- Apple cloud translates queries
- Apple cloud returns the search query to the AppleTV
- AppleTV performs search against all content libraries in Local Universal Search database.
It's probably not extraordinarily difficult to do, but it is a fairly radical architecture change to Universal Search.
And there's not a lot of incentive for Apple to do this. There's no financial gain. This feature only benefits people who don't buy content which generates a revenue stream for Apple (iTunes, HBO, Netflix, and all the other subscriptions that give Apple a cut). If anything, making it easier to use Plex libraries disincentivizes users to pay into those streaming revenue streams that Apple benefits from. So... probably a low priority for Apple.
TL;DR: Custom libraries in Universal Search are not gonna happen for a while. Almost certainly not outside a full-version update of tvOS. And it will be low-priority, as it would actively discourage people from paying for the content providers that Apple gets a cut from.