I think the delay in announcing Payne's replacement is to see length if any of O Brien's suspension. Having 4 genuine backrowers ( Henderson with O Connell gone can really only be considered a 2nd row now as they unlikely to put Mc Carthy on bench) is very low with potentially 3 games left and it would make more sense to bulk up that area rather than at best a 5th choice centre.
Indeed alternatively I would also think that Isaac Boss will be seriously looked at as well now to replace Payne for the same reason that having a 3rd choice scrum half covers more bases ( late short term injury or going forward concussion or suspension to either scrumhalf) at this stage of the tournament that a 5th choice centre ( Henshaw. Earls , Fitzgerald , Cave and if Sexton fit even Madigan)
Indeed alternatively I would also think that Isaac Boss will be seriously looked at as well now to replace Payne for the same reason that having a 3rd choice scrum half covers more bases ( late short term injury or going forward concussion or suspension to either scrumhalf) at this stage of the tournament that a 5th choice centre ( Henshaw. Earls , Fitzgerald , Cave and if Sexton fit even Madigan)