it's rather easy to relate to the issues you appear to have deciding on the "perfect" CMS for your project. So, yes, your posting makes sense (at least to me). Nevertheless, as far as your current project ("Deus Uno") is concerned, I believe you worry too much. From what I can see (thus far), it is not going to require features that wouldn't be provided by sNews (or NIbbleblog, or any other CMS available today).
As for the "design learning curve", there is no big difference between WordPress and sNews. Unless you are going to use the default theme, shipping with the respective package, you will have to know CSS and the structure of the individual pages. Since you are (apparently) going to use HTML5, however, you are beyond this stage already. I have switched between WordPress and sNews twice and no one was able to tell, as the front appeared and worked always the same. Just recently, I returned to sNews because I was tired of having to update WordPress in ridiculously short succession, without experiencing major improvements of the engine, but a lot of new issues with one plugin breaking another or my theme.
The more plugins you have to employ, the more troublesome it gets.
As for current or future development activity, none of us can seriously predict which CMS is going to survive. On the other hand, I have yet to learn of a single website that remained unmodified since its first launch. That's the point of development, after all. sNews has a lot of forks by now, but so far I haven't found one that would solve more issues than it caused. sNews, on the other hand, still has a number of caring users and developers - Keyrocks being only one of them.
The way you present "Deus Uno" right now, sNews is certainly one of the most efficient (if, admittedly, not the easiest to handle for the random user) and stable CMS to accomplish the task. By the time you really need a store front, your general requirements, as well as the provided features of sNews, may have changed utterly already. Who knows ...