actually, the last-minute and free aspect might ensure that it is a roaming event. i'll bet that some people will drink too much on monday afternoon and say "fuck it, don't feel like going anymore and the ticket was free so nothing is lost". others might get caught in traffic, or have a change in plans/overlooked plans, etc... and other than the sooper-dooper mystery headliner, none of the acts on the bill have a huge/rabid following so people might leave after their favorite leaves the stage. if the order on the announcement is correct, i could see how ted leo --> bob mould --> mystery headliner might not be everyone's cup of tea.
i remain hopeful.