Not an answer but a concern. I feel that the \obeylines\let^^M\linebreak
is of very limited use in the verse
environment. I ran some experiments, code below, which result in a 4 page document. I have not yet been able to post a graphic to SE; is it even possible for a 4 page document?
% verseprob5.tex SE 514469 verse in memoir without \\ line endings
% proposed answer but Herman: left justified
\documentclass[ebook]{memoir}
\begin{document}
\linenumberfrequency{10}
\verselinenumbersleft
\textbf{Default verse}
\begin{verse}%[\versewidth]\obeylines\let^^M\linebreak%
%\vin
Herman: \\
O'er every birth a star of fate presides, \\
And he that knows his orb of destiny, \\
May, by the changes of its radiance, tell \\
Whene'er his good or evil genius reigns. \\
This knowledge, earned by many a midnight vigil, \\
Has taught me that yon silver star is mine, \\
Which nightly, since I conn'd this wond'rous volume, \\
Hath dimm'd its fires, and warn'd me to forbear. \\
Yet have I still undaunted read, and now, \\
While pale and fitfully its beams shrink in, \\
The ingredients of a potent spell I mingle, \\
And but three drops of my own blood are wanting, \\
To give me proof that to my hests and bidding, \\
A spirit of dread ministry will come. \\
Why should the glorious planet fade at this? \\
\end{verse}
The above produces a result where every line is left-aligned and slightly
indented from the left margin. Lines are numbered.
\vspace{\baselineskip}
\textbf{Obeylines verse}
\linenumberfrequency{10}
\verselinenumbersleft
\setlength{\vgap}{0.42in}
\begin{verse}\obeylines\let^^M\linebreak%
\vin Herman:
O'er every birth a star of fate presides,
And he that knows his orb of destiny,
May, by the changes of its radiance, tell
Whene'er his good or evil genius reigns.
This knowledge, earned by many a midnight vigil,
Has taught me that yon silver star is mine,
Which nightly, since I conn'd this wond'rous volume,
Hath dimm'd its fires, and warn'd me to forbear.
Yet have I still undaunted read, and now,
While pale and fitfully its beams shrink in,
The ingredients of a potent spell I mingle,
And but three drops of my own blood are wanting,
To give me proof that to my hests and bidding,
A spirit of dread ministry will come.
Why should the glorious planet fade at this?
\end{verse}
The above produces an output where every line is of equal width (except the first)
and well indented from the left margin. The spacing between words varies widely.
\vspace{\baselineskip}
\textbf{0 leftmargin}
\setlength{\vgap}{0.42in}
%\setlength{\vgap}{0pt}
\setlength{\vleftmargin}{0pt}
\begin{verse}\obeylines\let^^M\linebreak%
\vin Herman:
O'er every birth a star of fate presides,
And he that knows his orb of destiny,
May, by the changes of its radiance, tell
Whene'er his good or evil genius reigns.
This knowledge, earned by many a midnight vigil,
Has taught me that yon silver star is mine,
Which nightly, since I conn'd this wond'rous volume,
Hath dimm'd its fires, and warn'd me to forbear.
Yet have I still undaunted read, and now,
While pale and fitfully its beams shrink in,
The ingredients of a potent spell I mingle,
And but three drops of my own blood are wanting,
To give me proof that to my hests and bidding,
A spirit of dread ministry will come.
Why should the glorious planet fade at this?
\end{verse}
The above produces an output of constant width (except for the first line)
with very wide inter-word spacing.
\vspace{\baselineskip}
\textbf{0 leftmargin, 0.7textwidth}
\setlength{\vgap}{0.42in}
%\setlength{\vgap}{0pt}
\setlength{\vleftmargin}{0pt}
\setlength{\versewidth}{0.7\textwidth}
\begin{verse}[\versewidth]\obeylines\let^^M\linebreak%
\vin
Herman:
O'er every birth a star of fate presides,
And he that knows his orb of destiny,
May, by the changes of its radiance, tell
Whene'er his good or evil genius reigns.
This knowledge, earned by many a midnight vigil,
Has taught me that yon silver star is mine,
Which nightly, since I conn'd this wond'rous volume,
Hath dimm'd its fires, and warn'd me to forbear.
Yet have I still undaunted read, and now,
While pale and fitfully its beams shrink in,
The ingredients of a potent spell I mingle,
And but three drops of my own blood are wanting,
To give me proof that to my hests and bidding,
A spirit of dread ministry will come.
Why should the glorious planet fade at this?
\end{verse}
The above produces an output of constant width (except for the first line)
with reasonable inter-word spacing, but well indented from the left margin.
\vspace{\baselineskip}
\textbf{minipage}
\begin{minipage}{0.7\textwidth}
Herman: \\
O'er every birth a star of fate presides,
And he that knows his orb of destiny,
May, by the changes of its radiance, tell
Whene'er his good or evil genius reigns.
This knowledge, earned by many a midnight vigil,
Has taught me that yon silver star is mine,
Which nightly, since I conn'd this wond'rous volume,
Hath dimm'd its fires, and warn'd me to forbear.
Yet have I still undaunted read, and now,
While pale and fitfully its beams shrink in,
The ingredients of a potent spell I mingle,
And but three drops of my own blood are wanting,
To give me proof that to my hests and bidding,
A spirit of dread ministry will come.
Why should the glorious planet fade at this?
\end{minipage}
\vspace{\baselineskip}
The above is typeset as prose in a narrow textwidth.
\end{document}
The regular verse
environment typesets each line to its natural width and also typesets line numbers.
The begin{verse} \obeylines\let^^M\linebreak
environments do not typeset line numbers. However, in all cases they produce a rectangular block of text obtained by changing the interword spacing on each line. To me this looks horrible, but by suitably changing the \versewidth
this can be minimised but still there will be unequal interword spaces.
Maybe it is alright for Devenagari, about which I know nothing except having seen it when hiking in Nepal 30 years ago, but for latin-based scripts I think not.