Hello. Rok from Proxy Studios (developer) here.
Sadly, we don't currently have plans for a demo, Jon.
Yup, we're on hexes. Squares were from earlier in development. There is more info available at our website at http://pandora.proxy-studios.com which I notice hasn't been linked yet. Though screenshot-wise, even those are outdated by now. We've been beta testing for more than half a year now, rolling for a release in November.
We definitely took the best things we could find or come up with. The interface in Civ 5 was immensely improved over Civ 4, the turn button in particular worked very well in my opinion. So we have that. With the added I-want-to-end-my-turn-and-I-don't-care-if-I-have-idle-units button alongside it. But we also weren't as persistent in hiding options like automate from workers or the production queue from the city screen -- we've streamlined it into one screen so you can manage your queue and purchase with the least amount of clicks.
If it helps any, Pandora will be priced around $30-40, most of Slitherine/Matrix Games seem to be around that price point too, as well as other games far and wide; I'm not sure what you mean by the business model of Matrix -- if it's overpricing of niche historical games, Pandora isn't historical or as niche. At least as far as Proxy Studios is concerned, if it goes well enough for an expansion, we would do that instead of mini expansions (i.e. DLC). Slitherine have actually been really great at giving us all the freedom to do Pandora how we want, all while giving us financial support.
Hope you guys get to try it out and enjoy it when the time comes!