Hi! Doc Watson was a double escape player, though I’m still not totally sure what type of motion he was using to do that. That’s an interview I was a little too late for.
But generally speaking, USX means you are making motion where only upstrokes go up in the air. So the last note on every string has to be an upstroke. That means you can’t pick all the notes in the tablature you’ve written out. Whenever you see a single note on a string, you know it can’t be done with a strictly USX or DSX motion while picking all the notes.
However, Tal Farlow the jazz legend had lots of lines that look like this, where he would use legato for the last note on the previous string, then do the single note with an upstroke. So you see lots of sequences where you have upstroke-pulloff or upstroke-slide on the previous string, then the upstroke by itself for the single note. So you can try working things out that way if you like. Who knows, it might sound cool.
What I will say is that this really isn’t a typical bluegrass approach. The simple answer is to say “use double escape”, but that is also an oversimplification. Because when they speed up, players like David Grier and Bryan Sutton actually use a mixture of motions where DSX is the main one, and most of the lines are worked out for downstroke string changes. For lines which don’t work that way, they sometimes use the legato approach as we’re talking about here, or they sometimes throw in brief “connector” motions that are double escape, often using a temporary turning motion of the arm or something else. It’s complicated.
This “DSX plus other stuff” approach seems to be very common in bluegrass, with players like Grier, Sutton, Jake Workman and lots of others using it. The other approach, again, is the double escape approach of players like Molly Tuttle. One of those two would be the most “bluegrass” way to play something like thiks.