I think all of this is sort of like predicting the future, time travel, etc. The answer is, nobody knows for sure! I don't care how you poop, there are potential pitfalls once you land in a nursing home. So much depends on the staffing levels and individual skills of the staff. Custodial care is nowhere near what skilled nursing (what you get for rehab after a surgery or acute hospitalization, for example). Basically, custodial care is only as good as its weakest link.
Plus, nobody knows if they are going to be in a nursing home for any length of time or what shape they will be in when they get there. One thing for sure, they ALL know how to clean up poop. Ileostomy or not, poop happens. This is especially true when you have a series of varied people taking care of you and they all are not equally skilled or careful. So, there will be detached bags, leaks, and episodes of incontinence because someone could not get to you in time. I am not sure it matters which oriface it is coming from.
Your sphincters get weaker the older you get. Fact of life. Your gut slows down too. So, maybe for us that is a blessing, where constipation is a big curse for most of the elderly! Plus, your skin gets thinner and more fragile as you age. This might make changing appliances more difficult to do without tearing the skin. No perfect solutions there.
Plus, who knows what new options may be found to assist us as the decades roll on? Maybe adult diaper technology will be awesome!
So, my thought is to do what makes sense for YOU in the present and near future, and let the distant future take care of itself. I worry more about having too much junk in my house for my kids to sift through when I am gone!