TXCREATE as specced out in EIP-7873 is designed to allow anyone to deploy a CREATE3-like EOF factory to a deterministic address on different chains. This is a core feature of the EOF devnet-1 plans and has been part of the mega spec for two years. It was removed from Prague as a concession to the size of the fork and was always intended to ship at some point. The current plan is to ship it with the Osaka specced EOF version.
Vitalik makes the best arguments for banning code introspection. It separates the representation of the contract from the consensus about its execution and outcome at the protocol level, allowing code to be transpiled to other formats, such as RISC-V. Allowing the code to enter or leave system memory locks in one particular representation of the contract as part of consensus.
Relying on a fixed gas schedule has been a problem for a long time and best practices are to not rely on it. EOF formalizes this recommendation in a way that allows future EVM repricings to have minimal impact on user code. There is a working group working on dramatic changes, including things like multi-dimensional pricing and code merkelization, which will have dramatic effects on the gas schedule as a whole.