I would have to consider carefully if I thought I was a high-enough quality candidate that it would be interpreted as a countersignal rather than a signal.

If I, gwern, specifically, were to apply, I might; because I know I am widely read on HN and I've talked with any number of YC partners etc, and they all know I take care in writing, and so me not capitalizing is a deliberate message rather than laziness or incompetence. They may or may not appreciate the message, but they won't infer the usual things, at least.

If I were anyone else and my application just one of thousands in the flood? You'd better believe I'd capitalize and spellcheck my YC application: https://gwern.net/blog/2023/good-writing