I would already declare any OSS contributions as a business cost and deduct them from my taxes? What above that is the suggestion?

I think this is a great idea and it just feels right. If you tax something, you have the challenge on how to distribute the money in a proper manner if it isn't repurposed to something else in the first place.

But having tax deductions solves the problem. There is an incentive to support open source, but the companies can decide themselves where the effort goes.