I think what is needed for lyrics and poetry is a special environment that preserves not only line breaks but initial indentation and interior spaces. reStructuredText has “line blocks” for this purpose (and for things like addresses), and I have adopted them in pandoc’s markdown. They look like this:
| The limerick packs laughs anatomical
| In space that is quite economical.
| But the good ones I've seen
| So seldom are clean
| And the clean ones so seldom are comical
| 200 Main St.
Since the cases where hard line breaks are typographically appropriate are relatively uncommon, special cases, there should be a special environment (like the above line blocks) that triggers them.