Did I miss something; is there an announced planned third edition? Or is this just hypothetical talk?
There isn't even a "2nd edition" except for Dominion and Intrigue; in places like these forums we have been calling the new-layout versions 2nd editions to distinguish them.
Jay decided to fix the layout of all expansions personally, due to subtle things and sometimes invisible things. It all started with the $3 on Courtier being wrong as reported by Ben King. Things will be more consistent now, and there will still lots of tiny things to fix; a go-to example, the black line below the banner of some Seaside cards e.g. Pearl Diver. He has already done Intrigue, Seaside, and Prosperity; I don't have a date for Intrigue or Seaside (since Prosperity is what people have asked about) but would guess it's mid-July, same as for Prosperity (and of course Intrigue will have a new cover).
So, when he's doing Dark Ages, well, it's an opportunity to fix Band of Misfits.
"Printing" could be a better term than "edition" for after-Intrigue sets, but all sets between Seaside and Guilds already received a second printing that fixed layouts, fonts, wordings, etc, didn't they? So this is another separate set of making-things-look-better that is now happening after the last one?
"Printing" would include printings with no changes, of which there have been many.
Yes, there were the original cards, then a version with improved layout, and now another version with more improved layout. The difference won't be as visible as last time; mostly it's fixing little inconsistencies, e.g. with the numbers on coins.