Huh? After joining up, broadcom produced the "brcmsmac" driver, which is now part of mainline, and modern broadcom devices typically work out of the box. Broadcom joining the Linux Foundation certainly had a lot of effect. It's just that these things take time. If nVidia makes the call that they are going to support OSS drivers today, it would likely take at least a year before anything percolated up to normal users.

Well based on the experience of when Adobe joined the Foundation, I'd say the impact is going to be pretty much zero.

Support for the few pieces of linux software that they used to make (prior to joining the Foundation) has now stopped/ gradually being wound down.