If the wording "NOT RECOMMENDED" were to become the
proverbial sand the IESG digs its heels in to make a stand,
then yes, I might be willing to say results of such tests are
considered "undefined" (or words to that effect). For one,
because it's rather a blanket-statement to say "MUST NOT"
against other uses of "v-spf1" records than intended, when
with 'other uses' we mean both current techniques and all
thinkable future uses. I mean, it is not unthinkable that
something will come along that, as part of its overall
scheme, checks against a header element they know is set to
the same value as the MAIL FROM entity (for which "v-spf1"
records could well be used). "NOT RECOMMENDED" therefore
still feels adequate enough to me.
It is not a permitted term of art.
Just pleasing the IESG isn't, and shouldn't ever be, enough.
As "not giving in to the IESG for the sake of not wanting to
give in to the IESG" is not a good enough reason to derail
the process, either. I believe in picking one's battles.
Its their ball you want to play with.
This is like saying that ignoring traffic speed limits is alright
because people might incidentally drive slow enough.
Speed limits are set through a government process which in the US at
least is the result of a democratic process and a democratic mandate.
Neither the SPF group nor the IESG have such a mandate.
You are asking them for something they are most unlikely to grant and
which will be meaningless if granted.