If you don't think Iowa would take Foster in a red hot minute, you're crazy.
We're having a good year but, last I checked, the last time we won the Big Ten was 40 years ago. I just don't think our collective assessment of what this program is matches up with reality very well sometimes.
As far as Foster himself goes, he's a kid who got a lot of attention and decided to stay home at one of the two in state high majors. He picked The Other Guys as far as HN is concerned. I'm sure he got the full court press from both schools, but saw something at ISU he liked. Prohm's obviously in over his head at the high major level, but he's no dummy - he apparently succeeded in painting a picture Foster found attractive.
For the immediate future, Iowa appears to be the more attractive place to be, but that's a very recent development. Given ISU's situation relative to Iowa's, it wouldn't be unreasonable to expect Iowa to remain more attractive for the duration of Foster's eligibility. Would that be enough to sway him? I don't know, but he likely has (not entirely unrealistic) expectations to not play out his eligibility anyways.
Stealing him would be awesome, but I personally don't think it's likely. If nothing else, from the Iowa perspective, making an overly aggressive play for him (or really, any play whatsoever) would risk poisoning the well. I don't think either school wants to be in a situation where they are having to consistently defend their existing roster by fending off overtures from the other high major in the state.