Answered here: Netlify Image CDN Now in Beta
Free and fair pricing
During the beta period, we’re not charging for the Netlify Image CDN. We do, however, plan to charge for Netlify Image CDN when it becomes generally available. We’ll be sure to communicate timelines clearly and our prices will be fair, including offering a generous free tier.
Also answered in the blog post:
We’ve started with AVIF and WebP, which have the best browser support, but we’re excited by new formats like JPEG XL and will be keeping an eye on browser support for these.
Not right now.
We can add a feature request for these 2 (+ the prevent resizes point from above), but we don’t know if/when that would be implemented.