I suspect that there will be a small number of commonly used variants in the DMG Toolkit Chapter, but not all of the ones from the 2014 DMG (many were nearly never used, though I bet that we will find at least one person complain that they're gone) and, with luck, maybe a new one or two.
I mean, technically, the entire Bastions Chapter is an Optional Rule, but if we're talking Variants to Rules that exist, I would expect to see "Gritty Healing", "Flanking", and one or two "Alternative Initiatives". Anything more would be a surprise.