Yah this is something I want the most. Even if it's just the ability to add a 'Sort name' option under properties for each game. For those that use Launch Box or similar programs you will know what I mean. So basically it will look like this:
- Tomb Raider
- Rise of the Tomb Raider
But the sort field is actually this:
- Tomb Raider 2013
- Tomb Raider 2015
However, regarding the current Steam client, one of the workarounds I do is to create a shortcut to the game you want to rename, then re-add the game into Steam as you would any non-Steam game by using the shortcut file as the .exe. Then it's only a matter of hiding the original.
This is not ideal but its a workaround, that unlike the text file editing method, does not disappear.