My advice:
Send a note to the 26 projects' lists (and/or directly to their PL/PMC?) reminding them of the need for the minimal effort to opt-in (it's not like jury duty or needing to put gas in a car if you want the car to continue to drive), and set a date after which they'll be summarily disabled from the simrel for non-compliance.
I say give them 2 weeks as you might be hitting people during summer vacation. Maybe make it due by Sept 4?
We could also consider having a heavy-handed "miss M2 and you're out [1]" policy for the annual June releases, and a "if you were in for June you can coast through the year without opting in again and again" policy for the other 3 releases, which aligns with the old annual simrel trains' opt-in process and gets around the apathy/vacation schedules.
[1] If kicked out they'd be required to opt back in by M3 (3 weeks later) or else miss being included in that quarterly GA release. Exceptions of course on a case-by-case basis if they grovel well enough to the EMO or PC. :D
#actionsHaveConsequences #soDoesInaction
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