I would imagine Arman is most likely if they don't give Ilia a title shot, since it would help sell a fight with Islam no matter who wins. Dana said they aren't giving Arman a shot again immediately after turning it down then pulling out the day before, so it would give him a chance to prove he can make the weight, or Ilia can prove he can handle a bigger wrestler or his punching power holds up against top LWs.
Timing works out ok too. If they announce it soon, it'll still be over a year between fights for Arman, and 7-8 months for Ilia depending on what card they put it on, while Islam just fought last month, so they could potentially put it on 315 which currently needs another big fight, then announce the title shot for the winner there for an August card, which would still only be 7 months between fights for Islam. Arman doesn't really have anyone else available.