Or... they should leave dungeons the way they are, and create more solo Scenarios for solo-only players for this sole reason.
Those players who wish to play solo and only solo in a MMORPG designed to be played with many other players. If so, the same amount of solo Scenarios should be created and drop gear with item level no quite at the level of respective dungeon difficulty, but close, so to not render current dungeons of any difficulty obsolete (as obsolete they already are compared to M+ and raiding gear) and provides a decently viable alternative for players who are anti-social.