If the holding power of TikTok is strong enough (which it just might be) then you might actually see teens start to switch to Android.
I'm not saying it's more likely that not, but I am saying I wouldn't be surprised. If you replace "one specific social media app" with "iMessage", it has already happened.
I don’t think the average American high school student has two smart phones one of which is a secret from their major source of income (their parents).
There's no use for a cellphone plan, we would just use wifi or hotspot from their main phone.