I’m not sure I understand. Do you mean that the proposer address could be part of the proposal body as opposed to the proposal header?
Fxed 
Phase 1 has no TrueBit protocol. Do you mean the phase 3 execution game with executors? If so, why is weakly secure?
We’re reducing consensus to its core: data availability. Execution (transactions, state, state transitions, validity, state roots, …) is a simpler deterministic execution game (not a consensus game). The default execution engine (the sharded EVM) will be added in phase 2, and will provide “meaning” to blobs that pay gas fees to use the EVM.
Alternative execution engines are possible, and this is facilitated by the natural evolution of consensus abstraction. Taking a historical perspective:
- Bitcoin (think “ASIC”)
- Enshrined-in-consensus dApp
- Account abstraction
- Ethereum 1.0 (think “CPU”)
- Enshrined-in-consensus dApp engine
- dApp abstraction
- Ethereum 2.0 (think “FPGA”)
- Enshrined-in-consensus data availability
- dApp engine abstraction