T138588: Execute the EditFormPreloadText hook in VE-MW on empty page load introduced support for the EditFormPreloadText hook that lets extensions preload text into the edit window. Although the hook call is still there, it has actually no effect. In the same file the condition in L507–509 prevents the text from being returned to the client. Removing the condition checking for the existence of the preload param fixes the issue, though I don't know if it doesn't introduce some other issues.

I'll submit a patch trying to tidy up this a bit. :)