After speaking with the various client teams, here are some of the reccuring thoughts that came up about how London went, how we can improve for the merge, and their priority in the next ~6 months.
One issue that was highlighted by most teams was the speed and lack of clear success metrics for the various testnet deployments. Specifically, the time from the various testnets to mainnet felt quick to teams (somewhat forced due to the difficulty bomb), and there was uncertainty about how to react when issues came up. Some suggestions of improvements were:
Another issue that was highlighted by most client teams (and several infratructure/tooling projects) was that changes were still being done to the JSON RPC API for London close to, or even after, the fork's mainnet activation. Similarly, it was hard for projects to quickly see what changes had actually been implemented outside of the consensus ones (described in EIPs). Some suggestions of improvements were:
Every team mentioned that, in addition to the consensus changes introduced by the merge, they have a lot of work to do on their clients to improve performance, modularize their architecture to support proof of stake, and onboard new developers.
When asked about whether they would like to have a "feature fork" in December (e.g. anything outside of the difficulty bomb pushback and, possibly, some constants adjustments for EIP-1559), all teams except one would rather not have it. 2 teams were explicitly against, one had people for and people against, but still needs to finalize London support, and one was in favor as long as it was done fully separate from the merge.
Given this, it seems reasonable to not have a feature fork in December, and instead point current EIP champions to the first post-merge fork (and likely push new EIPs to the fork beyond that).