The truly bizarre part about this is his fins now look exactly like a crowntail's. o.O But I've never heard of a VT regressing to crowntail before. I don't see any black edging that could mean infection/fin rot but nor do I see white regrowth meaning he's working his way back to being a VT. This is truly unique.
Since he seems to be acting perfectly normal, I'm very reluctant to suggest anything else other than what you are already doing. Keep in mind that AQ salt can only be used for about 14 days maximum, though. If you have any naturally dried oak leaves available to you, you can add one of those to his tank until the water turns tea colored. Indian Almond Leaf works best if you can find it. These add tannins that are beneficial for the healing process and help ward off infection.
Anhel is correct that frozen foods high in protein like bloodworms are great for the healing process. Feed 2-5 worms a day, alternating with his pellets.
If his behavior continues to be normal, then my best guess is somehow his genetic background kicked in and he reverted to crowntail.
Kudos to you for giving him such a great home and loving care.
As for the whiteish stuff you've been vacuuming up. That is probably a mixture of bacteria/slime that just naturally happens in tanks and shed excess slime coat. AQ salt helps to stimulate slime coat production so he is probably now shedding some of it off.