Update March 2025 in case anyone else has had this question and stumbles across this thread like I did…
Support for multiple axes has been implemented (Available HoloViews >= 1.17, requires Bokeh >=3.2) using overlay.opts(multi_y=True), as described in this example, which I copied here:
overlay = hv.Curve([1, 2, 3], vdims=['A']) * hv.Curve([2, 3, 4], vdims=['A']) * hv.Curve([3, 2, 1], vdims=['B'])
overlay.opts(multi_y=True)