It's a ridiculous change, and a ridiculous idea from start to finish. Hopefully they'll rethink it.
Weapon oil is cheap. It's much cheaper than elixirs or flasks and persists through death. If they were actually concerned with making raid consumables farming less of a burden, all they would have to do would be to make all consumables persist through death. If making elixirs persist would be 'diminishing the value of flasks' or some other nonsense then just apply it to food buffs. I spend several times more gold on buff food than I do on mana oil.