Hmm. If we use the idea of preparing some solution in advance in case the adventure is stalled, we could just make an 'adventure application' instead, meaning that a small form for adventures would be drafted that runners would have to submit. This could include premise summary, scope, involved characters if known in advance, 1-3 resolution options if the adventure has to be cut short and maybe a few more things.

Since this is in addition to setting up story elements it's an extra bit of work that can be avoided if it's something straightforward that could (and should) be done via plot ticket.

Not sure if this is a good solution, but if people automatically wanting to run adventures rather than those challenges/plot tickets is potential problem, it might help. Though, honestly? For the Ikokan Ship adventure I'd absolutely have preferred setting up the scene via Plot Ticket and then using the Challenge system for the robbers.