I'm going to risk your ire here
I used to be a huge supporter of tools like Duty Finders and Group Finders. But after seeing the long term damage they end up doing to MMORPGs - I have come to the conclusion I was wrong about them.
Now I recognize your idea is separate from these. And it doesn't sound bad. But I feel MMORPGs work best when players are encouraged to make friends with one another and do group content together. The MMO experience is just so much more satisfying as a result. But perhaps your idea would make for a good starting point for these kind of social beginnings to occur. Also it would help make it easier for a smaller group of friends to gain access to larger content by adding temporary members. So I can definitely see some good in your proposition.
But in the end I'll have to oppose it. I've just seen the negative effects tools similar to this end up having and how players tend to become overly-reliant on them. Also I worry it might start a step in the wrong direction and lead towards something worse.
I know it can be inconvenient and a pain often times - but I've decided group content on MMORPGs needs to be kept a friendly affair, and not done through generic means. Though I do support large scale content being made public