First of all, I just want to clarify - the standard streaming statuses/filter endpoint is not directly replaced by the webhooks-based Account Activity API; the webhooks will deliver account events on a per-user basis, rather than letting you filter on Tweets for many users.
If you’re looking for a higher-volume and more robust alternative to statuses/filter you probably want to look at the PowerTrack API (which is not webhook-based, but works in a similar fashion to the standard streaming connections).
In either case, unfortunately I don’t currently know why your form request would not have been replied to just yet.
Can you describe the exact limitation you’re hitting with the volume of users of your app?
