James has mentioned the "fisheye" I worked on as a possible feature for version 2.1.4. Other suggested names are welcome, such as the "magnifier."
I had this project working in 2015. based on 2.1.1, but set it aside for a long time. Lately I have reacquainted myself with my prototype and started the work of rebasing it onto later code. So far I have rebased it onto the Audacity-2.1.2 tag in the git repository, so that at least it past the wx3 migration and is easier to build.
It is in a branch in my fork called fisheye-on-2.1.2 and the latest commit is c9adf2f.
If you want to build it and try it, here is a summary of the user interface changes. Surely these details could be changed. I developed this on Windows before considering convenience on the Mac touchpad.
Key F toggles fieheye on and off.
Key G plays the fisheye.
Interface preferences have some new controls affecting fisheye appearance, including a choice among three styles for drawing the edges of the fisheye.
If you scrub, fisheye follows the play head. (Remember to Ctrl+Click to scrub in 2.1.2.)
Shift + Ctrl/Command + mouse wheel, with pointer in the fisheye, changes its the screen width.
Ctrl/Command + mouse wheel, with pointer in the fisheye, changes magnification inside it.
You can edit samples with the draw tool in the fisheye if the inner magnification is great enough, even if you cannot outside the fisheye.
Right-click in the fisheye, mouse movement, and right-click again makes coarse adjustement of the fisheye -- shifting the magnified window against an immobile, less magnified background.
Right-click in the fisheye, drag, and release makes fine adjustment of the fisheye -- shifting a window into an immobile, high magnification view of the track, while the backgound may move to adjust. (On Mac touchpad, control + three finger drag.)
Right-double-click in the fisheye recenters it about the clicked point.
Right-double-click and drag (possible to do on a Mac pad, with control key and pressure) makes "ultrafine adjustment" -- the display changes as with click-and-drag, but the fisheye moves slowly toward the mouse, not with it.