It would be great to move the re-index process to the background and keep the UI accessible for other actions.
GlikeG I think this is debatable. When this is happening, UI is out of sync from the actual state of library. Some operations might be harmful in that period. It is safer to block UI.
Andrey In this case, it would be best to block access to the folder that is re-indexing and leave free access to tens of other folders.
GlikeG Probably you are right. However the situation is not very frequent, so it will be very hard to prioritize this improvement among others.