If tabular figures are standard (assumed additional lining, oldstyle and tabular-oldstyle figures) Glyphs’s automatic feature generator writes sub @TF by @LF;
into the case feature what I find inappropriate here.
I think case should only switch (tabular) oldstyle to (tabular) lining.
But it should not question the proportional or tabular quality. sub @OSF by @LF; sub @TOSF by @TF;
Good question, the spec says whatever ‘works better with all-capital sequences or sets of lining figures’. It is about shifting or substituting punctuation, but also other subs if they prove to be more fitting for all-cap setting. It doesn’t say anything about tabularity, so I tend to agree with you.
It can be argued though that proportionality may make more sense in all caps. But that would depend on the design too. And what if the user specifically picked tabular figures…? So I guess you’re right.