UpdateStatisticsJob would be trivial to move to the worker role.

WorkItemCleanupJob would be trivial to move to the worker role, but it would also be obsolete if we weren't using background tasks in the first place.

LuceneIndexingJob is the trickier one.  But with the exploration of the Lucene index being served from blob storage, it seems possible too.  And then all web instances are always in sync.