Today, working with v7m, SVR1, and bsd2.11 all PDP11 ports, for example, will stay booted and operational for long periods under simulation.
This has certainly been my experience as well with mature, for the era, BSD ports. Most of the problems I have encountered have been with TCP/IP issues in 2.11BSD and Ultrix 3.1 related to traffic they were never expecting.
With these older UNIX variants, working with awk and even the classic shell tools is often problematic. Moreover resource constraints seem to be a persistent annoyance under simulation.
I think our expectations of a 16 bit Unix are going to be well out of proportion now. When 16 and 32 bit Unix systems existed side by side it was easy to consider the resource limitations of both when programming. Now that 16 bit systems have moved completely out of general end user space we only consider the constraints of the 32 and 64 bit systems that exist side by side.
Some of my interests lie in preserving early '90s hardware with original operating systems, and working within their constraints. Porting modern tools to SunOS 4 or Ultrix 4 or IRIX 4 (huh, everyone really was stuck on the same version) is a challenge but it can be done, as long as those tools do not necessarily rely on shared libraries. Backporting C99 to C89 is often not as difficult as it would seem, though it can sometimes be laborious. On the other hand, porting modern tools to my PDP 11/23 running 2.9BSD is a total non-starter for reasons that I am sure I do not have to elaborate upon here.
-Henry