There really isn't any reason to put a mini-Meijers downtown.

"Potentially down the road, we could bring this type of store to other urban markets," Guglielmi said. "The bottom line is, you can't take a 200,000-square-foot box and put it in a densely populated neighborhood. This gives us another option."
Detroit has plenty of neighborhoods which are not densely populated, many of them close to downtown. You aren't going to have a Meijer's in Detroit, even a little one, without a lot of parking, which is the last thing I want downtown. If there were no other place to put it, maybe they could justify the cost of building a parking structure into their site, but why would they do that if they didn't have to?

Downtown has the capacity to support numerous large retailers.
There is literally no evidence of this. Maybe it is true, and it is entirely possible will be true someday, but given that there still aren't that many people living downtown, that there are no large or even medium-size retailers downtown, and that there are none obviously anxious to locate there, this is a faith-based assertion.