Christian Villanueva is on the 40-man, but will be out of options in 2016. He has no chance of either a September call-up or a spot on the Winter roster. They could also release one or more of Beeler, Jokisch, Medina or Schlitter.
Hope you're right about a Contreras call-up---it would be interesting, but there are hurdles.
Beeler and Jokisch have 2016 options. Possible that either could be taken off winter 40-man and exposed to a waiver claim or the Rule 5. (No reason to "release" them as they would not be 6-year minor league free agents). But, considering depth issues in upper minors, seems unlikely at this point. We'll see how off-season 40-man shakes out soon. Always a fun topic.
Exposing either to a waiver claim in September to get Contreras to majors this season? Don't see that. Perhaps to make room for an August trade guy? Maybe, but not for Contreras to sit and get service time.
Villanueva seems a good bet to be traded in off-season. He has some value. But why expose Villanueva to a waiver claim in September just to bring up Contreras to sit/service time in September.? Don't see that either.
Schlitter is doing okay at Iowa, but Medina seems ahead of him now in the Iowa shuttle. We know there will be September pitching call-ups. Richards (if not claimed), Wada, who else? Edwards? Could be. Rosscup. Guessing we see either Schlitter or Medina, maybe both. If not, to get Contreras up? Don't see it.