Ethereum

“Plasma and EVM innovation are wide open. It's a huge opportunity because right now, almost no one is building in the Plasma space.”

- VB

Plasma TLDR  

Plasma offers more security than a Validium but less than a full rollup

In a Validium if the operator disappears, the coins are permanently stuck

In a full rollup if the operator disappears, all users can exit their funds securely back to L1

In Plasma if the operator disappears, only users who deposited over a week ago will be able to exit their funds (there’s different ways to design it, this is just one example)

/ethereum foundation | opinions are my own but more than likely they come from Vitalik's blog paragraph.xyz/@chaskin

The core validium trust assumption is not the operator staying around, but the data being available. If for example the state update requires a signature from an external DA committee, then the operator of the validium can't freeze user funds. They will get the data from the committee and submit to exit.