Hold the TDM event in late May, but as a plotline exclusive to TDMers, leaving them little (or no) overlap with the existing crew until they formally join.

PROS: TDMers can do their own thing and operate independently without any plot strain.

CONS: TDMers would be largely isolated from the existing crew and have to tag each other. Given that eastbound isn't a publicly advertised game, and the general flow of TDMers is small, this might discourage TDMers if they get little play. Doubling of mod work, meaning potential lags on arranging the travel Arc — though this can be minimised, with enough advance notice.