Everyone who works at Academia would love it if we were able to make advanced search free.
When we first decided to build a premium account, we also made the decision to not take anything out of the free account. Strange as it may seem, the free account never had full-text search because we couldn't justify the cost of building it (full-text search of 20MM PDFs at our traffic levels is expensive to operate). We built it for the premium account because people asked for it in our initial research - and we would love to be able to eventually move it into the free account.
On the team we all agree that we want to keep building premium features in order to make the platform sustainable. The author of this article takes the view that advanced search is not a feature that should be paid-for. My view is that we intend keep building features until we have something that is worthy of his support. The support of the academics who use and enjoy the platform, both in free and paid accounts, is what will keep it around and growing for the long term.