I am against this. These are plugins for a reason. If everyone is using a plugin, it should be in the core.
I don't want any plugins installed automatically or enabled by default.
(e.g. I'm not using the note tabs plugin.)
But we could create a button in the UI that will download a certain set of plugins that are deemed default/essential/must-have/whatever.
Update: another option would be to allow people to put a plugins-req.txt file in the profile dir that lists plugin ids and these will be installed, when you start up Joplin (in case they are not installed yet).