I'll experiment, especially if I can figure out a set of magic kpathsea paths to keep mkii and mkiv in parallel.
no need for that ; it is made to run in parallel, just an extra zip with mkiv and lua files ending up in base, and luatools.lua ending up in the script path; also, mkiv does not use kpse -)
Great. When the mkiv zip is available, I'll try it (tried poking around the pragma site but didn't find it). No kpse is indeed good news! About backward compatability, maybe the mkiv transition is the time to sacrifice backward compatability in a few instances where it makes the code or user interface simpler? One example off the top of my head is \setuppapersize[ABC] becoming equivalent to \setuppapersize[ABC][ABC] (rather than to \setuppapersize[ABC][A4]), and there are no doubt others. Or is the (understandable) policy of ConTeXt development that backward compatability is paramount? -Sanjoy `Never underestimate the evil of which men of power are capable.' --Bertrand Russell, _War Crimes in Vietnam_, chapter 1.