Version 1.0.13+ of iShowU V6 lets you dynamically zoom into the screen, in pro mode.

This is achieved by turning on the "Zoom via holding Option key" option, on any screen based layer.  Screen based layers include: Entire screen, selected area, applications and single window.

Once enabled, you can hold down the option key to zoom in by some amount. The exact amount can be set by the slider directly below the checkbox.

Note: this option requires Accessibility to be enabled for iShowU V6, in system settings.

A note re Selection Highlighting

If you are using selection highlighting (see General settings, inside iShowU), these will also follow!

Lets go through an example:

I've setup to record a chrome browser. The selection highlight will be around the window I've chosen.

Now, if I hold the option key, notice that the preview is now zoomed in, and that the selection rectangle is showing what portion I am focused on. The zoom will follow the mouse.