The keepgenerated option in default-web.xml DOES work properly.
In order to see the files it looks like you need a clean slate by undeploying the web modules and restarting DAS.
Once you've done that a deploy of a web-module will generate and keep the servlet java files in the right place in a "just-in-time" manner.
I.e. -- I was wrong. You do NOT need the --precompilejsp option for the deploy command.
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