Attempting to get the extra reach out of a Usmash just as a Dtilt followup isn't that useful though. This would only be feasible if Usmash was able to kill out of a Dtilt lock. Unfortunately, the percents that the Dtilt lock works aren't high enough to use the Usmash in such a way.
If it's for positioning and damage, then a grab functions the exact same way, but is far easier to do. At the percents that Dtilt locks are possible, you can definitely get at least one pummel in there, so the damage difference is negligible. I just wouldn't stale my Usmash when I could just grab, and pummels and grabs are generally good in refreshing the rest of your moveset. Usmash is always a decent killing move when it's fresh, so I like saving it on occasion. Even if a DACUS is an additional option, it's no different then Ftilting your opponent out of a Dtilt lock. Is it an option? Yes. Is it a good option? Not really.
It could certainly be funny to use for the lulz though.