Hey, new to the forums but certainly not to Dominion. I have a strong speculation regarding the Knights, although I need to wait for the secret history to confirm at least a part of it. I am guessing each knight is based on a friend, colleague, supporter, contributor, etc., of Donald X. That being said, and keeping in mind that Dark Ages was intended to be the last and final Dominion expansion planned in advance, I think that Donald, Jay, and other Dominion distributors intend to release promotional Dominion Knights cards in future years as special in-house promotional and print-and-play cards.
This reasoning is based on the Catan Card Game by KOSMOS, which every Christmas released a new Knight card based on someone associated with the development of the Cataniverse in-house that was afterward made available publicly as a print-and-play card. I believe they stopped this program in 2011 with the release of Rivals of Catan (or rather Princes of Catan), which rebooted the series and provided many opportunities to place said people in the game from the get-go.
I don't know if Donald himself would go to such lengths to include something like this, but the opportunity provided by Knights seems to be too much and the pile is really infinitely expandable with just the proviso that the pile must begin with 10 cards, with additional cards randomly removed. I think Donald will begin releasing promo Knights this year or next year, perhaps when the game is done. It may be Jay, or even a foreign distributor, that begins releasing a few a year, but I feel the Knights are the best way to do something like this.
What are others' thoughts on this matter?