I've said it before, just the time it takes to draw up the contracts can be expensive. The amount of money CBS could make from such deals would likely never amount to their costs, be they legal, accounting, or even fees they'd incur to do an audit. Just. Not. Worth. It. (I suppose they could draft a boilerplate take-it-or-leave-it agreement, but, again, the legal costs incurred if a breach occurred still likely wouldn't make it a profitable venture.)Let’s play what if for a moment.
...
1. Offer a reasonably priced, but limited, Star Trek license to fan productions....
More cost to create and host/make available said assets.3. Promote quality of licensed productions by offering a library of digital cgi assets they are able to access and use in their final product at no additional cost.
...more cost, further lowering any profit.6. Create an outlet, online, via their All Access streaming service, or any other method they wish, for the production to be viewed by audiences...
The act of getting into a business relationship with fan filmmakers could actually put CBS at greater risk of a lawsuit than the current "look the other way" policy. Right now, CBS can ignore the fan films until or if they become a nuisance, and then smack them with a C&D letter if they feel threatened. It's cheaper. Trust me, I was involved as an expert witness in an arbitration over just such an contract in the videogame industry, and sometimes a contract that was meant to protect you can come back and bite you on the tuchus.
In short, CBS would have to decide that there's enough profit for them—be that direct monetary of P.R. value—order to justify the cost and risks associated with making such a thing happen. Sans said upside, no incentive to do it.