In After Effects when you choose frames or timecode as the time display format in the timeline it displays the playhead position in your primary units (e.g. frames), and shows the alternative measurement (e.g. timecode) beneath in smaller type. I'd like to suggest that a similar thing could be implemented in Premiere.
The use case is that it's useful to see at a glance where you are in a timeline in both units, for example client notes tend to use timecode, whereas for animation I'm often working in frames.
I'd suggest that the alternative display was shown to the right of the primary playhead position. I'm aware that AE only has 2 time unit display types, whereas there are 4 I think in Premiere. Perhaps for frames and feet and frames the alt display would be timecode, and for timecode the alt would be frames. Or maybe the user could just alt-click through both to select which is show for either.
This is a QoL suggestion, but would make a fair difference to my working day. Cheers!