It doable but not at all trivial.
>It's well past the point of being worth forging
The news seem to indicate plenty of forgers still, e.g.:
https://www.europol.europa.eu/media-press/newsroom/news/poss...
>it is likely that future banknotes will use einks
einks are too expensive right now?
Maybe yes. But track their falling cost and you'll see where the price point intersects with near disposable cost. European transport tickets made of cheap plasticised card only took a couple of years to incorporate RFID - that's already a long way toward low cost "intelligent cash".
For a brief few weeks in the 1980s we had "phone cards" with stored, decrementable value that you could use a few times. Purely passive and using an optical technique to see where pressure had been applied to plastic (which turns milky). In Hungary in the communist era I saw tram tickets using ingenious mathematics (an ephemeral mechanical key set by the driver) and punched paper holes to provide multi-use.
It's amazing what can be done to make cheap or even disposable portable artifacts to transfer value.
I do recall that patents/trademarks/tech are owned by E-Ink inc., and one of the biggest reason for the cost is them gouging the market? That mechanism can keep high prices for a long time.
recall? gouging? You mean you have data showing is not just simple volume issues?