Why only the All Activity uses ajax to auto update ?

Why this can't be extended to personal AS or even AS created by admin, like the default Unread Content ?

All Activity is all activity sorted by time posted. When you start to introduce other filter options, like unread items, the order is unpredictable. There would be no way to auto-load content because you have no way of knowing if an item that is currently 5 slots down is now suddenly up top or if an item that hasn't been replied to in 3 years is now brand new. It would create a lot of user confusion because the approach is not linear as a human thinks.

Short version: we could do it but it would be very confusing to the user.

How? All content items has the unread mark and/or post date. The best and easy way to do it only ajax update when the admin/user creates an AS with Content I haven't read Read Status enabled.

The underlying reason is it's very efficient to check for new items in the All Activity feed. It's expensive (sometimes very expensive) to check for new items on other feeds that have complex filters set up, so we decided to only enable auto-updating on the main All Activity feed. 

I'm sorry. Can you explain, for example, an AS that mimics the old VNC (topics only) is more resource intensive than ALL other apps installed + status updates + likes + new users + reputation + profile photo change + following + whatever?

Filters? They're there to narrow results. If I have 1000 topics and my AS has 'only I posted', it goes down to 100 results!

Yes, running a query against 'unread items' for example is generally too intensive to query every few seconds like we do on All Activity (which is just grabbing by an index on date). The flexibility of the streams means people can come up with some really fine-tuned settings, and given we have to support lower-spec servers too, we can't put those on a 5 second timeout.

This claims may work with regular users. Nevermind. Just wanted to know.

Do you disagree?