Could be anything. I am inclined to think it’s Mueller-related due to scope (12 cases) and timing close to Stone’s indictment yesterday.

..at an unusual time.

happenings around the filings sure make it plausible.

the amount, specific court, and circumstances unfolding this week make it likely Mueller's involved. No guarantee, but fairly likely.

Secret until Jan 2021? Or would we know about it?

It would be up to Mueller.

There is one report, single-sourced I think, that Trump has already been indicted at the state level for Bayrock. See https://patribotics.blog/2017/05/14/exclusive-sealed-indictment-granted-against-donald-trump/ — Since then there have been many other sealed “cases” (not necessarily indictments) in D.C. that we assume are Mueller-related.

Personal opinion: given that Mueller demonstrably loves his country, he would be remiss to let us have another presidential election without the public having all the facts. I think we will see him act well before then, possibly soon, at which time he could unseal any number of indictments. I am hoping for a “twofer” to remove Pence as well—he was chosen by Manafort and is hiding his knowledge of Flynn.

With Pence would be great. Wonder what he would do/think then since God is putting him with trump now on a very special mission. He seems dumber than a stump to me.