I think one thing that is a bit different is that you are thinking of going to a recognized dressage sire that has the kneesier ™ action. What has been more typical imo is for a little bit of jumping blood to be introduced with Dutch and Holsteiner sires.
If you want the kneesier action, IMO you are safer to introduce it via bloodlines that also jump well, but that’s just some unsupported personal spec. It is true in general that kneesier action often goes hand in hand with a less elastic connection and more “headset” way of going for a horse. That’s not an “oh my stars - avoid that at all costs” observation, just one to keep in mind when making your decisions. Every single plus has a minus with it - pretty head, lovely, too teacup-y - mouth doesn’t hold double bridle well; refined and sensitive, nifty but sensitive in mind blowing surroundings - not necessarily great; etc. There’s nothing good that doesn’t have something you need to take into account with it. So it’s just nice to make sure you have a lot of elasticity and rideability coming in when you are adding in more knee and a difficult temperament can make a horse that isn’t as predisposed to a soft elastic connection a bit more difficult to get it from, since unlike some other things, you can’t “kick through” to create an elastic connection.
You could still extend your German lines some by maybe picking up some “b” blood (Bennidetto is a good looking boy - don’t know how his other lines would mesh with your mares).
A guy who looks like he will be adding some knee (and has the Holsteiner bloodlines to back that up) who I’ve had my eye on is Chequille. He’s already approved in multiple registries which migh help your situation. It’s early yet to say, but it looks as if he might also bring some elasticity and rideability and back up jumping talent to the table to go with the action.
But you might want to go ahead and contact some of the stations that have Dutch stallions either by frozen (or fresh, if any) that you are interested in and see what they can tell you. You might be able to get more first hand info trying to follow up on, say, what Idocus might have produced with some german line mares than overseas info, but maybe not.
Good luck - it’s been an interesting point and discussion