The main use-case for pristineless files is large, undiffable, undeltifiable files checked out from a box in the next rack unit over (= wide/cheap uplink and downlink).
Undiffable files will likely have svn:needs-lock on them, won't they? Is there a correlation between "has svn:needs-lock" and "doesn't need its pristine"? Does either of them imply the other (at least in most cases)? Should svn:needs-lock files that aren't locked have pristines (by default)? This could be viewed as a backwards-incompatible change, so assume the user has opted in to new behaviour.
