I agree there should be some sort of indication that gdebi-gtk is still reading the input file- and to do it on a different thread than the gtk thread, so you can still interact with the window.
I also experience slow startup times. For example, if I open the Atom
<https://atom.io> .deb, gdebi-gtk takes about 10 seconds to show the
package into and become responsive. In contrast, command line gdebi only
takes about a second. So there is probably potential to speed up startup
in general.
