The Plugins SDK now includes a plugin type called "ext" (along with hooks, layouttpl, portlets, themes, and webs).
The ext plugin works very similarly to the old ext environment. However, it's much smaller and lighter weight because the ext environment itself does not have to contain the whole portal code. The ext plugin only contains the differences (deltas). In addition the new ext plugin allows util-java and util-taglib to be customized.
To create a ext plugin, navigate to the /ext folder in the Plugins SDK from a command prompt and issue the following command:
create <name> <display-name>
create hello-world "Hello World Ext"
After deploying a ext plugin, the server must be restarted for the changes to take effect.