Perhaps ... but that would likely incur huge costs for Medium to set up, requiring more server space etc. Three times the cost of us just having one account.
And it still wouldn't solve the problem - which is that writers flock to Medium, hearing they can get paid.
And we still wouldn't have enough readers.
That's the problem right there, and changing membership plans won't fix it.
Also - although it's lovely here with no ads, there is an awful lot of 'free stuff' to read online, and especially now that Medium took away the three free reads, people go elsewhere. If they don't want to pay, they don't want to pay.
They'll go find other stuff in the zillions of blogs and online magazines and newspapers. They'll watch YouTube videos. They'll go anywhere that they can get free information and stories.