OK, here is the first ever formulation of my PhD research question (after I ditched the original idea about international communities in primary schools).

How do people successfully become members of an online learning community?

And the sub-quesion: ‘What problems and limitations stand in the way of successful membership?

Dave Wield suggested formulating the question in different ways, so here goes:
Why… do people have problems when forming online learning communities?
Where… are the most successful online learning communites found?
When… does a successful online learning community form?
How… do people become successful members of online learning communities?
What if… I had to design an ideal online learning community?