Would it be possible to integrate a changelog in the addon settings on the website, additionally to readme?
Yes, i can add that functionality.
But honestly i am not sure if it will be helpful at all. Since a lots of add-on barely uses version system. And adding screenshots is another challange.... ,
Adding change-logs will introduce another variable that might confuse devs.
Also since there is an option to add forum link, i think it is best to have change-logs there. You can just link the forum for anyone that is interested in change-logs.
But i can clearly see why you want a change-log system in the updater. But as it is right now, i am not sure if it will used by the majority.