They wouldn't remake Emerald and I have no idea why people keep thinking that.
R/S remakes with Emerald's additions, maybe.
But not Emerald.
Why would they not? just because the previous 2 remakes were in pairs doesn't mean that the next one must be in a pair too.
In the past they would come out with a third "enhanced" title such as Emerald, Platinum and Crystal.
Now they released a pair of games after BW, which were BW2.
IMO it is entirely possible that the next games be single and not paired versions.