I've tried to compile issues and proposals from #2513 and #9093:

Today VS Code supports two locations:

• floating on top of editor tabs (default)
• pinned to debug viewlet header (new option)

"floating" debug toolbar issues:

• floating debug toolbar can only be moved horizontally and its vertical position is not ideal
  • problem: floating debug toolbar hides tabs (but only in tab mode).
  • workaround: move floating debug toolbar to the left and make debug viewlet wide enough so that toolbar doesn't overlap with tabs.

"docked" debug toolbar issues:

• debug actions only available in debug viewlet
  • problem: you cannot use debug buttons when debug viewlet is not active
  • workaround: use F1 or keyboard shortcuts
• no debug configuration drop-down visible while debug session active
  • problem: another concurrent session cannot be easily started while one is active
  • workaround: use F1 or set "debug.showInStatusBar" to "onFirstSessionStart" and start session via quickpick
• no session drop-down visible if debug viewlet is too narrow
  • problem: it is not really obvious that the CALLSTACK view could be used for switching sessions in this situation
  • workaround: make debug viewlet wider

Proposed Debug Bar locations:

• in activity bar (Debug actions pane often blocks file names #2513 (comment))
• pinned to its own bar directly below the title bar (Debug actions pane often blocks file names #2513 (comment))
• like an actual toolbar (not floating) like VS (Debug actions pane often blocks file names #2513 (comment))
• in statusbar (Debug actions pane often blocks file names #2513 (comment))
• snap it to any edge along the editor view (Debug actions pane often blocks file names #2513 (comment))
• below the find box (Debug toolbar custom positioning #9093 (comment))
• under the debug viewlet header (Debug toolbar custom positioning #9093 (comment))
• float in the editor like the search widget (Debug toolbar custom positioning #9093 (comment))
• unanchored free floating (Debug toolbar custom positioning #9093 (comment))
• moves the debugger down into your code area (Debug actions pane often blocks file names #2513 (comment))

Important requirements:

• toolbar always visible (independent from which viewlet is active)
  • "docked" toolbar violates this
• toolbar should not hide anything
  • "floating" toolbar violates this

My take:

The two important requirements could be easily addressed by a global toolbar, but VS Code doesn't provide one.
Since it is difficult to find a good solution that obeys both requirements, I propose a two-pronged approach:

• improve "floating" toolbar (which will continue to be the default):

  • make it more suitable for editor tabs mode, e.g. by allowing to move it below the tabs, and/or
  • allow for unanchored free floating

• improve "docked" toolbar (which is most likely covered by Show debug sessions under a new split view section #49881):

  • don't overlap docked toolbar with viewlet header but create a new view "SESSIONS"
  • show debug actions in the SESSIONs header
  • move the session drop-down into the SESSIONs content
  • as long as there is only a single debug session there is no need to expand the SESSION view and all debug actions are available through in the header anyway

Let's start by improving the "floating" toolbar.