Hmm. Isn't Darksouls and bloodborne semi open world anyway...yeah. Hell the Dark souls is more open than some semi open like DA: Inquisition. A souls-borne open world would remove the metroid vania level design which is pretty much the core aspect of what makes souls games fun.
Kinda...you can move around freely to a certain degree, usually after you unlock some door/raise some gate, but I was thinking more of game that has DNA of Souls when it comes to "levels" and open/semi-open world/exploration of typical open-world RPG.
This is my wishful thinking f course, since I believe From is more than capable of creating such game that would not compromise core of what Souls games are, yet expanding on formula.