I created a new buildout from the branch 6.0 of the Plone buildout.coredev (https://github.com/plone/buildout.coredev) today. The buildout itself worked out of the box and I could create a new Plone site from it. I ran the Plone 6.0 a1 using Python 3.6.
I added some further packages to this buildout to check if the Plone add-on tdf.extensionuploadcenter would be compatible with the upcomming Plone 6.0 (and Python 3). I had to do this step by step. I run tests against every Plone add-on which I added to the buildout. There were no issues with the command ‘./bin/test -m <name of the add-on>’. Once I incorporated all Plone add-ons I could fire up Plone with ‘./bin/instance fg’. I created a new Plone site and installed the Plone add-ons ‘tdf.extensionuploadcenter‘ and ‘cioppino.twothumbs’. I could create a new ‘Extension Center’ and add a first ‘Extension Project’ to it without issues. Seemed there are no issues to catapult the LibreOffice Extensions Center (Site) into the Python 3 and Plone 6 world.