A demo for Dishonored 2 [official site] would've been more useful five months ago, back when people had no way to know without buying the game whether its initial performance problems would strike them. Still, a demo coming this Thursday will give a welcome look at the first three missions of Arkane's first-person supernatural stealth game. That's a good chunk of sneaking from a good game.
To be specific and leave no room for uncertainties that weren't left for me, I'll relay the official word from publishers Bethesda that the demo "will allow players to dive into the first three missions of the campaign as either Empress Emily Kaldwin or the royal protector, Corvo Attano." Presumably that's the introduction along with the missions to reach then infiltrate the Addermire Institute.
The demo is due Thursday, April 6th on Steam. Demo saves will carry over to the full version.
Following that initial flurry of performance panic, Arkane have kept on fixing up Dishonored 2. A new patch with more bug fixes arrived only last month. If performance and problems are now in a good-enough state that Bethesda are happy releasing a demo, perhaps they'll start nattering about expansions next. We've not heard anything about plans for story DLC but I wouldn't be surprised. It could be interesting, considering how ace the first game's side-story expansions were.
[Disclosure: My flatmate wrote for Dishonored 2 a little bit. I couldn't tell you what because, when we played together, we didn't reach any of her bits thanks mmmostly to me getting into messy fights after throwing glasses of whisky in people's faces.]
[Further disclosure: And in the game.]