Problem with Wikipedia specifically going all-in on a UK block is, due to the licence, there's nothing to stop someone circumventing the block to make a OSA-compliant Britipedia mirror with minimal effort.
It's really down to whether Wikipedia feels that compliance would go against the organization's principles. If so, blocking the UK is a perfectly reasonable thing to do. If another organization steps in to mirror Wikipedia in a way that complies with UK law, there's no downside for Wikipedia - they maintain their principles and the UK continues to have at least some access to free information.