idk if it is possible. or at least probable. we slowed it down to 1/4 speed and tried and couldnt get it. now dont disregard my statement because im not a pro...yet

. but if it is to be done with MK than it must be done within the first couple frames. seeing that a frame is 1/60 of a second and 1/4 speed would put a frame at 4/60 of a second or 1/15 which is only .07 seconds. in track .07 seconds is significant in any race 400m or less. now i can stop a watch within .07 seconds and clearly distinguish the distance and time between two runners at .07 seconds, however i cant manage the dash cancel to usmash with MK. im not trying to brag about my reflexes im just mathematically and realistically explaining the improbability of MKs ability to dash cancel to usmash. im leaving the possibility of this technique open, but to probability im saying no in a respect to the actual performance of this at .02 seconds in an actual tournament where frames are 1/60 seconds.
you could just dash and usmash which will slide you into your opponent while usmashing. this works under the same principle of a dash grab where you and your opponent will slide even while youre grabbing them.