Vitalik proposed the "L3 vision": L2 and L3 need to have different purposes, such as L2 for scaling and L3 for customized features, etc
Chain Catcher News, Ethereum co-founder Vitalik Buterin published an article titled "What kind of layer 3s make sense?" The article points out that stacking Rollups on top of Rollups cannot scale the network, meaning that using the same technology at both layers typically does not work well. A three-layer architecture with different purposes for the second and third layers can work.
Vitalik proposed three "L3 visions" using Starkware's three layers as an example, which mainly include:
L2 for scaling, L3 for customized features, such as privacy.
L2 for general scaling, L3 for custom scaling.
L2 for trustless scaling (Rollups), L3 for weakly trusted scaling (verification).
Vitalik added that it seems too early to define Layer 3 now, and the architecture of a multi-Rollup ecosystem is not set in stone; most discussions are only theoretical. (source link)