>> [: Carl Schwan :]
 >> I could add support for non-summit workflow, through this will add
 >> some complexity both in term of code as well as in the UX. But is
 >> there a reason why some teams don't use the summit workflow? Having
 >> only one version of a file to manage sounds easier.
 >
 > [: Albert Astals Cid :]
 > Because translating master (and summit as a consequence) is sometimes
 > chasing a never ending stream of changes that may not ever be released
 > because code gets changed, strings tweaked, added/removed, etc. So for
 > some teams they prefer to focus on things that are closer to released
 > status.

Insofar as one is (also) making a PO editor part of a system, I'd point
out that each summit message has an automatic comment `#. +> ...`,
listing the branch IDs where the message is found. For example:

     #. +> trunk6 stable6 stable5
     #: kcm_view_models.cpp:200
     #, kde-format
     msgid "Variant"
     msgstr ""

A list of branch IDs may be provided to the user to select, after which
the editor would hide the messages not contaning any of the selected
branch IDs.

(Lokalize can filter messages in this way through D-Bus, which is used
by a number of Pology sieves to open only the PO files and show only the
messages in them which have been matched by the sieve.)

-- 
Chusslove Illich (Часлав Илић)