Demo of the persistent-scrolling implementation:

@Sergey Sharybin (sergey) I will poke you for real review once I get the granular object type filter, so don't bother for now.

I'd love to see this, too.
I've even had my clumsy go at it some time ago and posting as reference (because there was some discussion/critique on UI that might be helpful?)
T43787: Outliner: Show/Hide By Type (part of even more clumsy tries here: T43282: OutlinerLove: a couple of goodies for the outliner)

Yay for filtering! Love it especially how it keeps the scrolling position and the UI doesn't jump around, this is something we should try to achieve everywhere in Blender.

As I understand, this is currently implemented for the Active View Layer and Collections views only. We should try to arrange these filtering options in the same nesting/dropdown layout they'd be when in other Outliner views. Only the filtering options that make sense for that view would show up (e.g. Collections view would list Objects, but not Sequence Strips or Scenes).

• Filter...
  • Objects
    • All
    • Lamp
    • Mesh
    • etc.
  • Groups
  • etc.

Update patch with object type filtering.

I would still like to figure out a way to handle:

• Collection filter
• State filter (active, visible, selected)

Also, be aware that children filtering is working, however we need to change how we draw children in the outliner (may as well be tackled by a separated patch). We should be able to tell these two scenarios apart:

1. Object A is in Collection 1, and its children B is not in collection 2
2. Object A and its children Object B are in Collection 1.

This was one of the core motivations for the outliner filtering by the way.

Demo of the current state: https://youtu.be/9Vz8UTLD0Q8

Also, after this patch gets merged (or before?) I need to integrate it with the other modes, and get rid of the unnecessary ones (Scene, Visible, Selected, Same Type, ...)

This is looking better and better, 2.8 Outliner is finally going to become what it should have always been, great work!

User suggestions

1 - Not sure if this fits into this this task, but as far as I know it is currently not possible to forcibly make a bunch of random items selectable, visible, or renderable from the Outliner.
I mean if a random selection of objects has a mix of different current renderability, selectability or visibility states, the only option in the context menu is Toggle #### said property, which obviously well toggles the current state.
This makes it so there is no easy way to match the state on all selected items if the current desired property state is not the same.

Is it possible to make it so that when clicking an item it makes all selected items match the active one state instead? I think this is closer to the expected result and matches behavior on other applications.
If not, alternatively add/replace context menu entries to something like Make Selectable, Make Visible, or Make Renderable?

2 - Would also be great if we could a "selection fill" option for the outliner.item_activate operator, as in the file manager file.select operator currently. You know, the regular Shift-Select item 1 to item 7 in the list and items 2,3,4,5 and 6 get selected too. Maybe also something akin to "Walk Select" file.select_walk for Keyboard arrow navigation.

Thanks for the great progress, keep up the excellent work!

@Sergey Sharybin (sergey) planning to merge this first thing in the morning if you are fine with it. Poke to @Julian Eisel (Severin) as well.

Bonus, planning to add this afterwards: P593