Confirmed that the following worked:
  1. Run: rm -rf /tmp/luatex-cache/   (your cache directory location will differ)
  2. Edit ./tex/texmf-context/tex/context/base/mkiv/scrn-ref.lua
  3. Replace line 15 to assign the empty function as Hans indicated
  4. Save the file
  5. Run: ./bin/mtxrun --generate
  6. Run: ./tex/texmf-linux-64/bin/context --make
Typesetting XML succeeds again.