These are all pretty reasonable factors.
I hope (probably in vain) that some suit in Paramount won't say "We left $600m on the table with STID vs IM3 or MoS, and therefore we can't count on it for a summer tentpole", leading to serious budget cuts and a probable Holiday Season release for the next movie. Don't care too much about the release date but I'd worry about the budget cuts w/r/t production values.
I doubt that another movie is off the table.
Interesting the production team has been quiet since opening weekend. I think they're in a state of shock.