I wonder if server-distributed DLLs might open up the clients to malware. That is, a server installs a DLL with malicious code in it and then since it sends the DLL to the clients the code is trusted and executed on the client side.
I also wonder if POI modlets might one-day actually work completely as a server-side modlet? They kind of work, kind of don't work, that way today as some information is not shared by the server.
There are some modlets I hate to see as server-side, such as UI modlets, but that's not an easy situation. What I mean is some people like individually customized UIs, some overhauls like to change the UI experience, and some servers like to change the UI experience. I prefer not to modify the UI and don't really care for servers that change it. I kind of wonder if there should be some kind of UI order of precedence, like local > server > overhaul/vanilla. That's probably too simplistic when it comes to overhauls since they can add elements not found elsewhere.