I wish it were otherwise, but configuration defaults cannot be changed as some people would not like it and it would badly interact with custom configurations.  We can add new themes and keysets, but that should be very rare.  We can consider adding bindings, though clashes with customizations are possible.

Do you have any documentation for you claims?  My impression is that Microsoft occasionally makes UI changes, so that 'Microsoft Standard' is a bit of a joke.  Maybe keys are an exception.

Ctrl+y is *not* recognized in Notepad.  ctrl+shift+z acts the same as ctrl_z.  Notepad++ recognizes both and lists both for Dedent in its
Scintilla mapper.  If it is not in use in the Windows keyset, adding it could be considered.

Before the first character on a line, in the absence of a selection, tab and backspace indent and dedent.  When there is a selection, tab and ctrl-] indent the selections and ctrl-[ dedents.  Shift-tab acts the same as tab.  I believe that tk, at least on Windows, does not recognize shift-tab as different from tab.  I know that this is true for some named keys, such as Enter.  (This stuff needs to be documented.)  Shift-tab works as you (and I) want in Notepad++, so this is not a Windows issue.