This is using some core api of qutebrowser, any change in qutebrowser can break those plugins ! They are relatively small so it should not be an issue to fix.
Replace the bookmark and quickmark of qutebrowser to use buku library.
Link the init_custom_plugins.py to your qutebrowser config dir.
ln -s ${pwd}/init_custom_plugins.py $XDG_CONFIG_HOME/qutebrowser/
In your config.py file add the following line :
config.source("init_custom_plugins.py")
Make the plugins to activate configurable in config.py