I very rarely travel DJ, but on my last trip with them, was assigned 1A. Was asked if prepared to assist in addition to being given a briefing.
Also, when travelling with QF, pax in overwing exit rows are also asked if willing to assist and are given a briefing. The quantity of the briefings sometimes vary.
This is a bit of a 'pet' of mine and very happy that this occurs, although I am concerned that most non-industry pax treat this with a degree of 'lip service', assuming it is only to meet some regulatory requirement.
History shows that if the proverbial hits the air circulating device, things will happen very quickly. Always assume the potential incapacitation of one or more F/A's.