I have experience in the technical ITG community, and nobody has called 3+ concurrent notes “hands” in years and years. This is because, with countersunk pads and the high speed of the stepcharts, nobody in their right mind would actually use hands for those.
“Brackets” seems to be the current name for these, although that name is also technique-dependent. Other alternatives are “Triples/Quads/Quints”, “Chords”, “Slams”, or “Multi-hits”.
The mission of 5.3 is to modernize Stepmania, after all. I hope this terminology is suitably updated.