I voted!
Work-around to hold you over until this is implemented on the Windows PC version:
Go to Settings. Select Widget from the tabs at the top. Its the last on the right. Once in there, on the right hand side, change the Status to Completed. Change the Number of updates to 50. Click on Update Changes just below that and then look the left and see what happens! You can scroll thru your completed shows in the order they were completed! You can do the same for Plan to Watch, etc.
While you can create a widget, you dont have to, u can just use this screen for additional sorting options.
p.s. the mobile app thats currently being worked on is already designed to allow you to sort your watchlists by "Last Updated". Date when Android/IOS app version available: -- its too soon to give an idea when, as its in development. Status is TBD.