I guess you wouldn't have expected such a drastic change of course. Me neither. I have always been of the idea that the freemium business model was the one that best suited my way of thinking, and I am still convinced of that, but sometimes needs change rapidly, and when it does happen, action has to be taken proactively.
My income isn't regular yet, and to date, the continued investment of resources in the SiteTree project has had a return only on the emotional level. I personally live mostly on food-for-mind, so giving up on the project wasn't an option, but I am a human being with the same needs as yours, therefore I had to come to a resolution. On balance, transitioning SiteTree to a paid-for plugin was unavoidable.
SiteTree 7.0 will be released in the second half of June, and it will be a nest of new functionalities. It will introduce the ability to build stand-alone image and video sitemaps, and it will incorporate Wonder Leaf in its entirety.
The upgrade will be available as part of an Access Pass, a yearly subscription that will also give you access to Multilingual Leaf at no extra cost — Multilingual Leaf is the add-on that makes SiteTree compatible with WPML. The Pass will be purchasable at 20€, but for the first month I will offer a 50% discount on it.
I confide in the hope that you will keep being a SiteTree lover, but if you choose not to, I thank you very much for having used SiteTree.