Wow, this is quite an impressive release!
I compared this release against the 3.5.4 release by running an html5 transformation on 89 books in our deliverable set.
Here are the results of the linux time command on a transformation with/without -Dparallel=true:
% time ./dita-ot-3.6/bin/dita -i dita-digital/dita/icvrefman.ditamap -f html5 -o oo
177.620u 10.915s 1:48.15 174.3%
% time ./dita-ot-3.6/bin/dita -i dita-digital/dita/icvrefman.ditamap -f html5 -o oo -Dparallel=true
242.156u 12.990s 1:26.75 294.1%
There was definitely more parallel processing going on (green), but the decrease in wall clock time was less dramatic (yellow)
But heck, with default improvements like this, who needs more?