I’m guessing this is a no-go simply due to data risks (though, hey, single selection → multiple is less risky than plenty of other conversions…right? =), but having label as a forced single field sidesteps the reality that many, many releases are co-releases, collaborations, or otherwise released by >1 label.
It’s a bit of clutter and a touch of data anti-hygiene to end up with, say, “Atlantic/Rhino” as well as Atlantic and Rhino (plus the possibilities of ending up also having “Rhino/Atlantic”—to say nothing of “Atlantic, Rhino”, “Atlantic; Rhino” and so on).
I always see the value of these kinds of data fields as being a way to look for everything released by a label, or to see what label might dominate in a collection, or some variation on these—both of which are rendered impossible with a single datafield and multiple labels involved (in Collector only, you can always do a filter by “contains ‘$LABEL’”, of course, but that takes knowing some RegEx to avoid pulling in, say, “Anticon” alongside "Anti"¹—and I’ve been told by enough people that enjoying RegEx is a sign that something is wrong with me…)
But nothing ventured, nothing gained, right? It definitely won’t happen if I don’t ask, even if it won’t happen if I actually do as well.
¹Which should be—and usually is, as far as I’ve seen—“Anti-”, which saves the issue, but the principle stands, even if that wasn’t the perfect example