Why would that be a problem though? The Kraken endpoint only works for the currently authenticated user and requires the scope for viewing subscription for said user. That’s all developers want from that endpoint, just the same functionality we have in Kraken, but now in Helix.
Being able to get information for an arbitrary set of emotes is useful, but knowing specifically what the currently authenticated has access to is useful for providing a better UI experience for things like emote intellisense, as we only want to show the emotes that user can actually use in chat. Otherwise all you could show to the user was the global emotes and the emotes for their channel.
The only other way I can think of to get this same effect would be to query for all the channels that user is subscribed, then make batch calls for all the emote sets for those channels.