Okay, here is what I think.
The field house concept is a unique one and in order for it to work for a proper stadium it will have to be executed perfectly. Consider what the height of the roof would have to be in order to accommodate punts and soccer goalies booting the ball, oh and javelin throwing

Add to this a concourse that would need to be functional for both food and beverage and washroom facilities and i really think that it's a big ask. Google the worlds largest field house or multi-sport facility and nothing really comes up. Because the facilities don't really exist. The closest I could find is is the Aspire Zone in Doha Qatar and more specifically the Aspire Dome.

Credit:
http://internationalcup.alkass.net/

Credit: Wikipedia
I also think that the prospect of a summer Olympic games in Calgary is WAY out of the question. If Calgarians don't have an appetite for tax funded venues then the Olympics are in no way going to happen here. The number of venues needed for a summer games are well beyond what ever this NEXT project might be. No point going there.
I agree that a fieldhouse has the ability to attract tourism dollars in the form of both amateur and elite sports. There is a shortage of venues for sure. Think of International Friendly soccer games and what the draw for something like that might be.
I am very curious to see what happens Tuesday. I am also hoping someone calls King out for being so Vague. Let's call this the Ryugyong Arena project