ChatGPT is a better search product than google, traffic decline to SEO-optimized clickbait websites proves this; they're absolutely 100% going to monetize free tier chatgpt with ads, why would they not? Advertising is 70-90% of Google's stable revenue, they would be insane to leave that money on the table. The question is, given they already have paid-tier products, will they offer ad-free products still? Google always offered their products for free in favor of getting more eyeballs to drive ad revenue, because nobody was willing to pay for a search engine. In this instance, the paid product was offered up front, so hopefully paid products continue to offer an ad-free tier (which I'm happy to pay for, fuck ads).
Interestingly, Facebook just started offering a paid tier in... I think the UK? Hopefully that takes off and we see that across other advertising-funded , previously "free only" tier services. We got Youtube Premium during the pandemic and that's been a tremendous value for money.