Accepted as legal tender where?
It's already legal tender in El Salvador and in the Central African Republic.
I reckon the US will probably be one of the last places where it would be legal tender, as the US is the strongest fiat at the moment.
But let's remember that before the USD there was the British Pound, and the Spanish Real. Things change, and they change faster and faster. I can see that there won't be any next new fiat, but instead there would be a Bitcoin standard to replace USD dominance.
Of course the USA won't want that to happen so it won't make it a legal tender there.
Not the same period though. Sure those were times when things were a bit different and they dominated that period, but that was because they took their money everywhere they went and that caused it to be bigger than everything else.
Right now we are in a global world, you might live on the opposite side of the world to me and we are talking here, internet made it like we are one big nation instead of so many different nations, we can chat and work and pay all at the same time in a minute. This means if USD is the biggest right now, during this period, then it's harder to drop that down. Bitcoin has a chance, just not a lot of chance to do so.