I think a lot of this depends on the definition of a 'flight'.
If we do a RTS (Return To Stand) in the jet, if we've moved under our own power we have to record the time in the aircraft log and it counts as a sector. Subsequently, we have to take that into account in terms of FTLs on the day. Does this count towards the 100/900 running totals? Our tracking systems think it does.
Occasionally there are 'taxiing duties', which involve moving stuff around the airport. That counts for 'duty at the behest of the employer' but not for flying hours in our records.
Taking those two paragraphs together it would appear (in the company I work for, anyway) that taxiing time with the intention of flight is 'loggable', and indeed should be logged. We have plenty of lawyers, so one would assume that they'd mulled this one over.
Re: logging time spent in the queue at the holding point (commercial ops.), like at JFK, I think the relevant authorities might take a rather dim view should they need to check your logbook after an incident and it didn't match up with "official" block times. Especially if you'd busted 100/900 in the process...