You might consider taking a look at Celo. They have ultra-light client support [0], it's proof-of-stake with single-block finality, and they run a true EVM that you can program in Solidity. It's mobile-first but since it's fundamentally a fork of Ethereum it is also web3 compatible -- there's a metamask fork here that should soon be functional [1]. Gas is payable in multiple ERC20 tokens, and should remain cheap as the network scales. Not sure if this falls under your "ethereum killers that can do 10x transactions/second" so apologies for shilling if it's not interesting to you.

[0] https://docs.celo.org/celo-codebase/protocol/plumo

[1] https://github.com/dsrvlabs/celo-extension-wallet

We're building this, but on Bitcoin ("Plasma but as a framework for dapps" [with a focus on developer experience]) [0]. There's already robust infrastructure for L2 contracts in Bitcoin-land, and we've already heavily optimized the L1 to prepare for the load that a global, ubiquitous solution would need.

Honestly, I see no use for Ethereum (or other Turing Complete L1s) looking forward — smart contracts can be purely peer-to-peer, with the only pressure applied to L1 being dispute resolution. By pushing complex contracts up into Layer 2, we can keep the dangerous, money-destroying, theft-enabling Turing machines away from the main chain.

[0]: https://fabric.pub

If you want a Layer2 plasma with similar guarantees to Ethereum (account based, not zero knowledge) then you may like Gluon.network once they roll out EVM support.