Or the maintenance cost could be significantly increased.
I would love something like this: any failed patent suit doubles the maintenance cost for all patents owned by the entity which owns that patent. The effect would be transferable (i.e. if they sold the patent to some other company, that company's costs would double) and it would stack (i.e. failing with the same patent twice, or owning 2 such patents would quadruple your maintenance costs.) The effect would last for some fixed period of time, so if the patent were truly valuable, a company could opt to keep it anyway.
Obviously, that would make any patent involved in a failed lawsuit highly undesirable, so no one would want to buy it. It would also mean that shell companies wouldn't be able to send the patent back to a company dedicated to simply amassing patents.