I don’t mind Detroit playing in a dome. All of the “cold weather” teams should have some sort of solution in order to extend the MLS season.
Playing in a fully enclosed stadium ensures they'll have solid attendance in months like March and November when it can still/already be below freezing out. Not having the possibility to play "outdoors" might be unfavorable but I dont see how it's a deal breaker in any sense.
As much as Detroit fills a nice geographic spot between Chicago and Detroit and north of Columbus, I would only accept them with a SSS. The minimum exception i would make is the "Montreal Method". You could play your first 1 or 2 games at Ford, then move outdoors. Having said that, the weather in Detroit can't be too much different than Toronto and you have seen what they have done outdoors in the last 2 years of playoffs and finals in December. Now of course, if the league would shorten it schedule by shortening the playoffs and getting rid of the mid year friendlies, you could end earlier than December and outdoors should be a problem. I would think fall is still better than spring, as rain is worse for both the game and fans than just plain cold.