N.B. I would probably actually buy a lot more games if such an option were implemented, so consider that a monetary incentive for getting this fixed, if that helps at all...
@kisak-valve do you still monitor feature requests on here?
Nothing extracted yet.
Your system information
Steam client version (build number or date):

(I took a screenshot because the text on this dialog didn't seem to be selectable or copyable)
Distribution (e.g. Ubuntu): macOS (which I realize isn't Linux, but this is should be consistent across platforms)
Opted into Steam client beta?: No
Have you checked for system updates?: No
Please describe your issue in as much detail as possible:
I am trying to limit the impact of Steam on my hard disk space, and as such, I would prefer to download smaller games rather than larger ones. One way I would like to do this would be to sort my wishlist by filesize so I can give preference to smaller games when I feel like buying something new. Unfortunately, there seems to be no way to do so currently, as can be seen in the following screenshot:

Steps for reproducing this issue: