3DS not getting a patch, seemingly
I experienced Mega Man Legacy Collection on the Xbox One with little in the way of problems, but PS4 owners have been complaining about an audio issue for months now. Finally, Capcom has pushed an update that will presumably smooth over this concerns, as well as add Japanese language and Rockman version support (the latter of which the 3DS launched with).
According to producer Frank Cifaldi, the 3DS edition is not going to get any further patches (at least for now), but the PC version will get a patch at some point in the future.
Frank Cifaldi [Twitter]