Hi,

The latest version of notmuch (actually for quite a while now) ships
with an alternate nicely threaded search interface called notmuch-tree.
Earlier this was in contrib, but now it is part of core.  So I thought
it would be nice to use that to follow org-notmuch links.

Attached are two patches: the first adds the customize options, the
second provides a function that uses notmuch-tree to follow links.  The
defaults are set to the old behaviour, so this should not cause any
surprises.

I have done some light testing, and the patches seem to behave nicely.

Cheers,

-- 
Suvayu

Open source is the future. It sets us free.