If they keep going in the direction of a somewhat-traditional family-friendly musical that is based on a more-well-known property, CHARLIE BROWN would make sense, but I wonder if ABC's rights to the animated specials would conflict (either legally or strategically.)
I humbly propose BIG RIVER as a thought, which covers family-friendly and based on more familiar material, or 1776 (family-friendly, certainly 3 hrs long, and likely relevant after a Presidential election.) But Encores! could have aims for 1776 that would pre-empt NBC.
Words don't deserve that kind of malarkey. They're innocent, neutral, precise, standing for this, describing that, meaning the other, so if you look after them you can build bridges across incomprehension and chaos. But when they get their corners knocked off, they're no good anymore…I don't think writers are sacred, but words are. They deserve respect. If you get the right ones in the right order, you can nudge the world a little.