Tim,
I'll add it to the list. It won't be hard to configure what your asking for, but...there might be more to the story when different table layouts are used.
For example, we've started to produce and make public horizontal timetables for the first time (the idea being that this format would work better in a screen reader for viz impaired --
http://trimet.org/schedules/w/t1100_0.html). With that layout, for trip based events, I found that I needed to mark *all the stops* in a given trip with the footnote symbol, since a footnote on just the first stop would not be seen (or heard) when looking at times for another stop (eg: a lower row in this orientation), since reading left-to-right, they'd be no footnote otherwise.
BTW, the logic I used in placing the symbol was the left-most column
for trip based events (what I considered to be trip based), and to put
the note into other columns when the event happened at the stop: eg -
http://trimet.org/schedules/w/t1109_0.htm (see the A symbol on the
second stop).
Cheers,
Frank
ps, the current release TTPUB generated horizontal (called vertical) tables too...but does not have the logic (yet) to place the symbol on all stops in the trip.