I look at the Bill Grundfest (@BillGrundfest) & Alan Silverberg (@You2Gov) recommendation to drop jargon and speak plainly as inspired for Gov20LA. Any activist can lose their message in jargon. Often it takes many attempts to create a workable message. Then it can take many attempts to cross the chasm to the customers who need the message most, e.g., the electorate. If information and communication were perfect, we would not have entire industries based on them.
So I see the Grundfest Manifesto more as practical insight from his TV and screenwriting experience: first, make an elevator pitch.
I never heard Grundfest mention "elevator pitch" (probably because it's screenwriting jargon), but the pitch is what it takes to get in the door in screenwriting which has some of the same cutthroat and passive aggressive qualities as politics: no producer wants to waste their own time or say No to any screenwriter, but neither does any producer want to miss a good thing. So screenwriters need to give producers a quick one-liner taste (elevator pitch) of their story. The jargon-free elevator pitch is the door opener.
So I believe producer Bill Grundfest and Gov20LA organizer Alan Silverberg are just being realistic about communication in screenwriting... and politics. Drop the jargon, and find the elevator pitch for Gov20(LA). Define Gov20 in language that resonates. Jargon-free is an important and inspired message to help define the movement now, rather than later when poor communication habits could make any jargon harder to shrug off.