Firstly, there is the challenge of predicting the number of unspent transaction outputs (UTXOs) that might be needed in the future to cover fees for pre-signed contracts. The flexibility to adjust this estimate in proportion to the value at risk in a smart contract provides some scalability, but it does not fully resolve the issue of future-proofing.

Another point of concern is the use of additional bits within the protocol. More bits can lead to increased fingerprinting risks, implying a potential compromise on privacy and security. This increase in identifiable information could have implications for users' anonymity and the traceability of transactions.

Moreover, ongoing development and deployment may yield new insights that could influence the evolution of the protocol. The experience gained from working on Version 3 (V3) of the protocol may highlight the need for expanded topologies, which could result in complex interactions between multiple components. Furthermore, direct upgrades to V3 might be considered, or the introduction of new bits could signify policies for securing constructs similar to SIGHASH_SINGLE|ACP. Such policies could potentially provide more extensive coverage for various cases, enhancing the robustness and functionality of the protocol.

These discussions reflect an understanding that the Bitcoin protocol must evolve cautiously, with careful consideration of the implications each change may have on the system's security, usability, and scalability.