For now, FG Roster Resource projects Williams to make a start Sunday.
DFA'ing Littell lets teams claim him off waivers if there's a contender interested or we release him and he can sign with any team on new terms, including a minor league deal. IF he's claimed, then another team picks up his contract, and if he's not, we pay him the rest of the year even if he's then signed (the new team pays MLB minimum). TBH, it's kind of a solid for Littell. He gets to go to any contender that would have him, and we aren't extracting anything for him.
I will guess that Mikolas might have gotten a similar offer from the Nats front office, but may have said he'd rather just pitch here where he has a job. He will keep that job rather than a Kent or a Perales moving up in August to take his rotation slot. Those guys may pitch a bit in September if some of the other pitchers a innings limited.