The https://github.com/plone/ploneconf2016.policy add-on is what we used to build the 2016.ploneconf.org, 2017.ploneconf.org, and 2018.ploneconf.org sites. I updated it to work with Plone 5.2 and Python 3.
(@cekk and @pnicolli did something a bit different using similar content types but their own Gatsby front end for 2019.ploneconf.org)
Related: we have a client at sixfeetup.com who needs a multiconference site, and we are prototyping it using ploneconf2016.policy’s content types as a base, and will create a subsite for each conference.
Yes, we managed it in a different way, trying to have something generic, which you can find here: https://github.com/collective/ploneconf.policy
Then we built specific customizations for 2019, which you can find here: https://github.com/collective/ploneconf.policy2019
This is all baked into: https://github.com/collective/ploneconf.buildout
All of these packages are already Plone 5.2 and Python 3 compatible.
On top of that, this is the gatsby public-facing site: https://github.com/collective/ploneconf-gatsby