Consistency is key. I support this change.

Apparently, StreetComplete is one of only two projects that uses none: https://taginfo.openstreetmap.org/tags/sidewalk=none#projects

no is slightly more often used: https://taginfo.openstreetmap.org/keys/sidewalk#values

Vespucci also uses no: https://taginfo.openstreetmap.org/tags/sidewalk=no#projects

Note that =none has experienced a recent rise of 100K tags since January, which presumably is due to the popularity of StreetComplete.

Haha, StreetComplete vs everyone else, who wins? ;-)

none will have to be supported by any data consumer pretty sure for forever, so it doesn't really matter which value is used. But it's good if all editors tag the same thing the same, so approved.