What happens? Nothing. Absolutely nothing.
What happens to perceptions? Probably something.
There's always mistrust of the biggest player. If Apple become's the most valuable technology company in the world, their propensity to control their stack will be even more a focus for the media.
I think Microsoft will relish being an underdog for a change: "Clearly we're not a monopoly. We're not even the biggest technology company in the world."
Even if both companies change nothing, they will be seen differently.