I would first recommend perhaps polling the community on if the changes you would like to implement are even desired.
For me personally, events aren’t very important and the last one was very bad. I am fine with passive events where you collect item and turn in for additional reward. These other tracking features you highlight are meaningless to me.
I think adding elemental stones would be a giant mistake - the power of our characters is already quite high.
In terms of actual content… perhaps Frintezza, Valakas, Hellbound tower, etc. could be added with current client? If that’s the case I think it is more than enough to keep sever interesting for many more years.