[adrianmonk]

I wonder if it might be a minor performance issue in the worst case.

Without keepalive, you create a new connection and pay the latency costs of doing so. With keepalive, there's a chance you try to reuse an old connection, and it fails, which requires round trips to learn about, and you still have the latency of creating a new connection. So more total latency in that case.

It seems it would improve the average case but make the worst case slightly worse. If your keepalive timeout is short, maybe it would come up often enough to matter.