Yes, Deckard being a human is thematically important. But so is raising the question of whether he might be a replicant.
Also, is there not a dedicated Blade Runner thread?
There have been a few Blade Runner threads on here over the years - this is one of most recent/relevant threads from the ‘Off Topic’ section:-
http://originaltrilogy.com/topic/Blade-Runner-Versions/id/47837/page/1