I don't know. I think people underestimate the general audiences' tolerance for far-out fantasy elements. Look at the blockbuster success of the PIRATES OF THE CARIBEAN movies, HARRY POTTER, TWILIGHT, CLASH OF THE TITANS,TRANSFORMERS, etc.
If audiences can accept giant alien robots that turn into cars, not to mention sea monsters and teenage werewolves, I think they can handle a magic alien ring or two . . . .
Don't you think a film sets a tone for itself, though? Those movies firmly planted themselves with the fantasy/alien sci-fi tone from the first frame. If that's done, audiences accept that. It's when you start pulling the tone rug out from under the audience that they start to balk a little bit. Favreau has set a very particular tone in his films, and that tone has been an attempt to ground whatever fantastic elements there are in a realistic world. There's only so far you can push that before everything starts to seem different and an audience rejects it.
It's not impossible to change the tone of a film series, but it is difficult. The first series of Batman films had a steady change of tone, and look what happened there.![]()
Except they had Thor's hammer IN THE MOVIE that pretty much affects the tone, or are you telling me Norse Gods are more realistic than alien tech.