I often find myself staring at this non-progress bar, when I open an old wallet:
<img width="274" alt="Schermafbeelding 2020-09-16 om 12 54 14" src="https://user-images.githubusercontent.com/10217/93328232-c3bd7400-f81b-11ea-98c1-51680f56c9f7.png">
Ideally the wallet should open and then display a non-blocking rescan progress bar. With some explanation that new transactions won't show up until it's complete.