2 suggestions

[Jungle]

1. When drive combos enabled for explorer panel and MC window size is quite small, buttons (tree, root etc) are not visible.

I see 3 ways to resolve this.
  a) Additional button (like arrow button in old MS Office toolbars) may appear which shows something like popup menu with inaccessible buttons
  b) Bar wrap, i.e. buttons which don't fit bar width should be shown at next line
  c) Additional toolbar (like drive bar)

2. Current file info. This was already suggested but it is especially actual now because of list mode.

In list view mode you can't see current file info (size, date, attr ...), so maybe a section in status bar can be used for that?

[Mathias (Author)]

1. When drive combos enabled for explorer panel and MC window size is quite small, buttons (tree, root etc) are not visible.

I see 3 ways to resolve this.
  a) Additional button (like arrow button in old MS Office toolbars) may appear which shows something like popup menu with inaccessible buttons
  b) Bar wrap, i.e. buttons which don't fit bar width should be shown at next line
  c) Additional toolbar (like drive bar)

Yes, That is something would like to fix. But there is no easy way to fix so that it will auto correct it self if the window is resized. 
All good solution would require a lot of work. And I would categorize it is a minor issue and it would cost to much develop time to fix it.
But I put it on the list. So maybe I get a good idea someday and can fix it in a easy way.

2. Current file info. This was already suggested but it is especially actual now because of list mode.
In list view mode you can't see current file info (size, date, attr ...), so maybe a section in status bar can be used for that?

Yes, Something like that is planned. I will push it higher up on the todo list.

[Jungle]

Concerning p1. Indeed it is a minor issue. But i've already mentioned that monitors become wider, so maybe vertical panels/elements could be used somewhere?

[Mathias (Author)]

If you have a wide monitor then you will probably not shrink the program so much so that icons disappear.

I been think about adding something like that.  Problem is that it is not easy to add it into the way everything work now since a lot of the UI is built dynamic at runtime.

(Why do I not have unlimited time to spend on developing new things. So much to add, so little time..)

[Jungle]

If you have a wide monitor then you will probably not shrink the program so much so that icons disappear.

Yes. I've faced that situation on clean system with 4:3 monitor and no video drivers. Indeed it is probably rare situation.
I just look at all that ribbon software and wonder why so much horizontal space is not used. Well, maybe i use that software in a wrong way