[Martijn]

you can get an add-on list through JSON-RPC. not sure if you can also get the current addon version with it.
if you can you could save current list. then start comparing it every X amount of time and that way notice if there's an updated version installed.

even better would be that we kept a list of recent updated add-on (or store addon update date). Perhaps something for the future.

Thanks for the ideas.
I was hoping that addon updates were "notified" like video updates so I can handle them in the onNotification() method of the Monitor class which I already use. I just checked that out and it turns out this is not currently the case so something like what you suggested would probably be the way to go.

Maybe some one can add this to the onNotification() method to at least know there are add-ons updated or new ones available, depending on how you have set repo updates.
Then you can catch that, notify the user who can go to the add-on manager to update them manually. If auto update is set you could then grab a new list of add-ons and then mention the updated ones.

Edit:
Implementation would be something like this https://github.com/xbmc/xbmc/pull/4766/files
and i think relevant file to add it to would be
https://github.com/xbmc/xbmc/blob/master...y.cpp#L319 (some where after this line of code. next line does the GUI popup).
This would at least get the add-on update available.
So if some one could take a stab at it?

Sorry for the bit off topic.