Gotcha. IIRC search is taken care of by their rewriting of querystrings. Comments and things like WooCommerce aren't going to work, but if you want to do that kind of stuff SSGs aren't going to cut it - to do any kind of per-user processing you need some kind of system to do that processing, which SSGs aren't going to provide. We're thinking about using HardyPress for some of our non-profit clients because we can probably work with something like fixed donation amount buttons and Stripe.js.
