Recalling many flights in Siberia & Kazakhstan in the old days, when almost every pax stands up during the taxi:
I tried it a few times, and since I'm prone to motion sickness in road transport, I found it rather unpleasant standing up (never mind if it's dangerous, or not, I just thought I might vomit!)
Admittedly it was mostly Tupolevs and Antonovs which are rather bumpy when taxiing across poorly maintained, pitted concrete aprons...