This is a terrible idea.
First, it's an outdoor stadium and if the weather goes south, it will be a disaster.
Second, given the likelihood of protests, etc., having an open-admission rally in a public stadium that large is just begging for trouble. Too many people to vet, no real ability to remove people who protest...it could get really ugly.
On the flip side, I think it's premature/unfair to compare this with Obama's event, where the Greek trappings and ornateness of the set was worthy of mockery. If Trump doesn't do it that way, I don't have an issue with it other than the practical concerns stated above. I'd personally hold off on those comparisons until we know what the actual set will look like.
