to being honest i prefer a demo than an open beta, because the OB are usually restricted to certain users (i.e. people that preorder the game) or people with special suscriptions (gold and plus, in consoles), also in these you can play for a limited time. But Demos are available to public use without restriction, like both KOF XIV demos or like DOA4 and DOA5+ in vita. About online? screw that.
Iirc the SCVI open beta was available for everyone, so there are chances that an open beta of DOA6 would be playable for people with and without PS+. I like fighting people more in DOA than the cpu, plus, the online mode of this game will be improved upon compared to DOA5's, so it wouldn't be such a pain playing vs most people, as good connections are rare to find at times.
i can agree with it at some extent. In my case i have a regular-to-irregular internet connection, and the only fighting game i've played in fluid capacity (no lag nor input lag) has been virtua fighter 5 (xbox 360). i had two matches today of DOA5LR and while i hadn't lag, i suffered of horrible input lag. That's why i in particular have no interest in online stuff.
in the other hand, open betas tend to be limited time, so you can play from X day to Y day, why not just put it free so everyone can test the game, liked it and once they are used to it they can jump in and buy it? in example, the rumble roses XX demo was my selling point in the same way that Soul Caibur IV (my first SC, btw), DOA4, skullgirls and DOA5 alpha demo convinced my to buy these games.