> There are numerous defenses a kit maker could use ...
What makes you think kit makers have the moolah to afford the lawyers required for the court challenge?
It's a matter of is it cheaper to cease and desist, litigate or settle? If the kit makers cease and desist, they effectively exit the kit making business. With respect to a decision to litigate or settle, a settlement on terms described by the story would mean the kitmakers effectivly exit the market as kids won't be saving soda bottle return money for a $40 model. So, if the kitmakers want to continue mass marketing kits, they will have to litigate.
I don't think the case would ever make it to trial as the kit makers would likely win summary judgement of non-infringement due to multiple invalidity defenses.
All that is my non-legal opinion based on personal experience.