The 220px thumbnails are too small considering the great amount of high resolution displays  and the growing number of dpi on mobile devices. I think it is mandatory to change this in the next two years or so. Otherwise the user experience will drop significantly.
Currently there are discussions about the technical problems on how to implement this:
- T43712#469014 states some caching problems when setting the standard thumbnail width for each wiki separately and (possibly) different. Therefore I'd suggest to change the default globally.
- Another proposal  suggests to "store only preferred-size thumbnails indefinitely"
In the past a few site requests had community consensus but were closed as "WONTFIX" due to server performance issues. (See bug 47332 for example)
Though community consensus is needed for a possible patch of this bug to be merged the technical details should be discussed first.