I'm not sure there could be any sort of legitimate threat to them, but I could definitely see a Netflix situation playing out. That is a popular upstart temporarily seems poised to take over, but then suffers from extreme levels of interference from bigger players who artificially hold the upstart down while they desperately catch up and then ultimately come at least equal while the Netflix equivalent is mostly a shell of what it could've been.
Never underestimate how much buckets and buckets of cash reserves can overcome even incredibly out of touch laziness when it comes to competing with any start ups. Apple in particular could probably afford to let competitors get a decade ahead and still be able to come back based on the ridiculous amount of cash they have to float their business along with.