The good thing about the Olympics is there are no BYEs for defending champions, so Mu and McLaughlin HAVE to run at the Trials if they want to run in Paris.
But I think it won't be until the start of June before we know whether Sydney intends to run or not. Looking at her programme the last couple of seasons, it's perfectly reasonable to assume she will not race until then. She may possibly do a race before then, but unlikely. She will do one, or two meets, and then the Trials.
At the moment, the schedule allows her to attempt the 400/400mh double. Whether she actually does this, I am less certain of. But the schedule gives her that option and I think they wont decide until late whether she enters both. If she does both, they'll see how her body reacts, and then they have options for Paris. I personally believe she will be mad to double, because of the overlap. Past 200/400 doubles have been successful largely because of limited overlap, but the 400mh and 400m are on alternating, consecutive days in Paris. On top of that she has to face big talents in Miller-Uibo, Bol etc.
My instinct is she will run in Paris. If she is successful - i.e. at least 2 gold medals, as anything else would be seen as a disappointment - I think she will retire before LA28 and be a commentator there. If she isn't successful (injury/DNS, or gets beaten) then I could see her take a break, and come back for LA28.