I don't expect wiki to be free. Free means you're the product, not the customer. But I see no reason why it should be expensive for each of us to have hundreds of small sites reflecting the hundreds of conversations that interest us.
I've recast wiki as something small, easy and personal. I hope every individual can own a space there which serves their needs and no others.
A small wiki addresses one point of view in one conversation. It stands alone but seeks not to trap readers within its bounds.
An easy wiki starts and grows by rearranging small ideas until they jell into something of lasting value.
A personal wiki speaks with the authority earned by its owner as identified by its domain.
If we are to own a wiki on infrastructure we only rent then we must be able to move to better infrastructure whenever we so choose.