No need. Canonical folks see it.
Changing a default application is not done lightly by the Ubuntu Desktop Team. The changes affect millions of installs, disrupting happy user habits and/or company workflows. The potential backlash of millions of angry users creates a rather high threshold to seriously consider change proposals.
Rhythmbox may crash for you. But that doesn’t mean it crashes for everybody.
Similarly, Lollipop may crash or fail for others, but not you.
If you are really serious about proposing this change, then start looking at previous similar discussions on the Ubuntu-Desktop mailing list. Here is the starting point discussion on that list when Rhythmbox was originally added. Many of the same issues will arise.
A change request may go in directions you don’t anticipate. Example: A new player may be selected that is neither Rhythmbox nor Lollipop but something else. Remember to keep your discussion civil. Be patient. Be positive. Proposals that are argumentative or devolve into I-am-right-and-you-are-wrong are often simply dropped without further comment.