I think it's fucked up that the federal government introduces a policy and then tells the states "you figure it out", indeed.
But I think it would be reasonable to add a time commitment to the ticket that will allow enough revenue to be collected after the period of intensive use (referring to the line in the German article: "Die Option zur monatlichen Kündbarkeit werde intensiver als erwartet genutzt. Das nimmt den Verkehrsunternehmen Planungssicherheit.") The Probe BahnCard still has a minimum running period of 3 months, so making D-Ticket's running period at least three months would be understandable. I can't say if that will be enough to keep the pricetag of 49 Euro even remotely sustainable of course.
referring to the line in the German article: "Die Option zur monatlichen Kündbarkeit werde intensiver als erwartet genutzt. Das nimmt den Verkehrsunternehmen Planungssicherheit.")
This part of the article is a little misleading, if not manipulative.
For example, in Bavaria many young people have switched to their discounted variants recently. And it was absolultely predictable that they would do that.
Everywhere, people were looking for options to cancel the subscription in a flexible way (and restart it at later times). That was visible right from start, and by now, the companies have gotten used to it.