What lisp machine articles often miss is contrast to other related projects.
Complete introspectable systems: How does the experience compare with using Pharo Smalltalk today? Sure, it doesn't provide a kernel, but it's a pretty complete* system that's very reflective and open to modification.
Running a lisp userland: There are Common Lisp replacements for Emacs, CL window managers, and one or two Lisp Machine style GUI libraries (CLIM). However, most Lispers seem to be happy using other WMs and Emacs. Do the CL applications miss something that the Lisp Machine environment provided, or were the alternatives more compelling somehow?
Other Lisp Machines: The MIT CADR is open source and available online[1]. Lisp Machine articles seem to focus on Symbolics software, what is that the CADR lacks? rms allegedly reimplemented many Symbolics features on MIT Lisp machines.
I'm often struck by how many Lisp Machine features have been implemented on other systems (e.g. CLIM, versioned file systems) yet haven't gained many users. There must be stories here.
1: http://www.unlambda.com/cadr/
*: Of the developers I've met, Emacs hackers seem to live in Emacs more than Smalltalkers in their image. For example, there are multiple Emacs twitter packages, but I've not seen any applications (only libraries) for tweeting from inside a Smalltalk image. I'm not sure what this says about the respective environments.