Open Channel Before Swap Filled

Now that I think of it, it could by a good idea to reverse the direction of the channels, I.e. B opens a channel to A, C to B and so on. This way, a user could sign up for a swap, fund a channel, and then forget about it for the time being, without having to react when the last participant is found.

The issue will be re-balancing, depending on how long it takes for all channels to confirm. The longer you have a channel open, the more chances of it being used/drained and ultimately making re-balancing more difficult.

You're right, that would be a downside. Maybe the intention to rebalance could be made a restriction for a new swap. In my experience (with 4 swaps!!), rebalancing is hit-and-miss already.