This is very cool! And I say that as someone who was in iCE in the early 1990s ;)
The baud scrolling and SAUCE support are nicely done, and "drag a zip here" is top-tier magic, though when I tried dragging in an old iCE pack's zip file, it only showed one ANSI inside there; I was expecting a file picker.
Feature suggestions: "Show invisible text" toggle and an option to switch between 16-color background mode and 8-color background mode with blink support. You're already parsing the SAUCE which has an "iCE colors" boolean; you can use this to control the default for the latter setting.
Details: https://forum.16colo.rs/t/ice-colors-or-blinking-text/27