I don't know where i should place it.
After some changes to the new default.json rig, the mhx2 exporter didn't wants to work anymore.
Didn't knew where i could post it, so i prepared a fix by myself.
As reference i used the changes of the other exporters.
I'm not familiar with python but it seems to work properly, if someone needs the fix too, i have attached it to this thread.
How to:
Go in makehuman\plugins\9_export_mhx2
Rename the old mh2mhxt.py
delete mh2mhxt.pyc (if presented, it will be recompiled at next running of the script)
and place the new mh2mhxt.py, in this folder.
Have fun

EDIT: My file is obsolete so I deleted it, load fixed file from Thomas @ https://bitbucket.org/ThomasMakeHuman/m ... /downloads