I think ChatGPT’s moat is mostly “it’s the first AI thing I used/heard about”. It’s not clear to me that’s enough to maintain their market share if OpenAI is the only one mixing in ads. It does seem to work elsewhere, though; consumers have brand loyalty to a fault, and often for the brand they started with.

That’s basically Google’s search moat too.

The question is how many users have developed intimate personal relationships and have named their ChatGPT, and how many of them would bounce to a different provider if some line is crossed (of which advertising could be one)?

Anecdata isn't data, but I know several individuals who have and thus are even more unlikely to churn than mere brand loyalty on the level of eg Coca-Cola.