Since the pioneer's days of Freddie Laker, Longhaul Lowcost has always and only gone in one direction.
If there was money to be made in long haul low cost, Michael O'Leary would have been onto it years ago and Ryanair would be operating widebodies. Would a company which would charge for using the lavatory onboard if it could get away with it pass up a money making opportunity ?
The companies which stayed close to the basic low cost model such as Southwest, Ryanair and Easyjet have mostly been successful. Those that went longhaul with widebodies mostly haven't.
The A321LR and B737 MAX will be interesting as routes beyond the traditional out and back same day will be possible with the advantage that they can still be used on the regular network if the longer stuff doesn't work out.