Adding my voice to this and keeping the topic alive as this is indeed a basic requirement for the API. I mean the followers count is the very first KPI for a channel, so as soon as you’re doing analytics on a large scale it’s a pain to do it without a batch call (and becomes just impossible with API quotas applied).
Aren’t you guys keeping a “static” count of the followers in the users infos that you update every time there is a new follower?
Also you’re saying this is for performance reasons, but if you don’t put it in the user endpoint, we’re all gonna have to call the “users follows” endpoint 100 times more anyway (which, besides, is heavier at least data-size wise), so doesn’t look like you’re gonna get any performance gain from that 
If you don’t want to decrease performance for calls to the users endpoint that are not interested in followers count, could you consider the solution of adding an optional “with_followers_count=1” parameter for those of us who will have to get that one way or another anyway?
This seems to be a win-win: calls to the API are divided by 100 (for you, and for us), and you don’t decrease performance for the “default” users endpoint ; so it’s a 100% positive impact for the API performance.
How does that sound @geardrops? 