For those interested, I've just release nano-mu4e 1.0:
https://github.com/rougier/nano-mu4e
It is a minor mode for mu4e that offer an alternative layout for
headers view when threads are enabled. There are still a few display
synchronization hiccups because mu4e is mostly asynchronous and not all
functions signal when they're finished (especially mu4e-execute-all).
Header line on the screenshot is not part of the mode but I'll add it at
some point.
NOTE: "g" (tag thread root), "G" (tag message) "t" (toggle TODO tag on
thread root) "T" (toggle message TODO) and "C-l" (refresh view) are bound
when you activate the mode.
Nicolas
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Nicolas P. Rougier ——
www.labri.fr/perso/nrougier
Institute of Neurodegenerative Diseases, Bordeaux