While opening multiple files don’t wait till the last file is open. Instead, open the first file and give control to user. Then in background open remaining files with low priority threads.
Consider a scenario where user is trying to view a file which is yet to open in editor or still opening. Every file must have indicator whether it is in opening state. If user chooses a file which is in opening state, the concerned file should be opened immediately and resume normal open files process.
May be syntax highlighting etc. can be delayed till the time file is actually viewed by user.