Interesting discussion in today's Mpls Star Tribune about the current Dome and all of the things housed in the facility, including Gopher and other amateur baseball, prep sports, and community recreation.
http://www.startribune.com/politics/...7PQLanchO7DiUr
Leads one to ponder how this will affect the discussion about a new Vikings stadium. I'm of two minds on this one. The first approach, and most likely, is a facility with a roof, retractable or not (though aesthetically I prefer a fixed roof facility). You build it with a moving stands system so that baseball can be played there. This would also accommodate the ability to play host to Final Fours/NCAA Regionals and/or a Super Bowl. I think this is the most likely option.
A second approach, which I don't believe I've heard anyone espouse, is to build a new open-air football stadium for the Vikings on the current Dome location. A true, NFC-North stadium, with 65-70K seats, adequate premium seating, a heated grass field, purple seats, etc. This, is what I believe, the Vikings would truly want in the end. The cost of this would probably not be more than $650 to $700 million, especially if the designers were creative in using existing infrastructure, including the existing lower bowl of the dome.
As mentioned above by RRJack, maybe this approach could be coupled with the construction of an approximately 15K seat indoor arena....similar to Telenor Arena in Norway (see photo).
http://en.wikipedia.org/wiki/Telenor_Arena
Basically, all you would need is a large warehouse/hangar style building that could be used for amateur baseball, prep sports including the prep bowl and other state championships, minor league soccer, and other community uses. It would obviously need a higher roof than Telenor Arena, but the concept would be the same. It wouldn't need to be fancy, and if built correctly and structurally well, could serve the community for many years. This would replicate every feature of the current dome except the ability to host a Final Four or Super Bowl, which is such an infrequent thing that I don't believe it to be a major sticking point. I don't know where you could put it exactly, but maybe somewhere adjacent to the Fairgrounds, which is a good central location.
Cost wise, it looks like Telenor was built for approximately $100 million US. Even if it was $150 million, throwing that on top of an outdoor stadium probably still wouldn't equal the price tag of a new facility with a retractable roof. As for long-term operating costs, you could probably just moth-ball the facility all summer as well.
I don't know if anyone has ever thought of this, but this would be a great solution in my mind.