Darashiva on 03 April 2018
I'd say the best option for IPs the publishers are not using would be to outsource them to smaller developers, while still holding the publishing rights to them, because let's face it, no publisher is going to willingly just give up any of their intellectual properties for free.
This way those unused IPs would not only remain relevant and in use, but it would also give the publishers an incentive to make use of them, as they could minimize their costs for them while also making profit by publishing them.
