Funny you should mention that, IIRC a KA-10 processor (first of the DEC10 line) had two protect/relocate register sets. One for the 'high' segment, usually pure code, and one for the 'low', mixed code and data. I did spend some time playing with KA-10 s/n 9, which had only one set. In the early days, the registes were optional, as was the byte-pointer and floating point hardware.
Yes. A DECsystem10 KA-10 processor would happily do 40+ users with160kwords of -core-. That's using a 1Mword drum as swap device and with about 44k resident as the monitor (o/s). Of course, it wasn't a speed demon compared to systems ten years later, but for the time, it was great.
Also, since a "batch process" effectively means performing some processing based on pre-written instructions, as opposed to interactive instructions, a PDP-8 could certainly do them. Not fast, mind you, but it could.