AIUI the match was kicked around between George (II) August and the widowed Hedvig. Then Georg (I) Ludwig heard about the affair that she was having with some or other Swedish courtier and decided against it.
In 1701 George I was still married to his cousin (and it's unlikely he WON'T since that match was financially motivated, and his dad pushed it AIUI), and I'm not sure the divorce was recognized outside Hannover (think Karl I of Palatinate's divorce from Charlotte of Hesse). So, the main way to get the marriage to happen is to have Georg August die before marrying or having kids. Even then, I think Georg might be wary of tying himself to a second wife who has a reputation.