Have you EVEN read the title??
They are not sharing this information with private entity aka. opt-in/out. They made partnership research & development agreement in with GSK with invest over $300MM. 23and me is not sharing our data outside their fences BUT this agreement will let them bring GSK into their playground and do all sorts of stuff with your DNA.
Worst case they will just buy the whole 23andMe as a company and once they own it, still your data technically haven't been opted-in/out anywhere, but Glaxo will do whatever they pleased with it :)