The Tyranid filler maps would be a PvE style of match that would be mixed in with the pvp maps to give some variety. The idea is to take regular pvp maps and put tyranid spawners on objective points. Players have to clear out the tyranids and recap the points. They would have limited lives to clear out the infestation. These maps would allow for shorter que times and greater variety. These tyranid matches could appear 10% of the time even if there is no overflow. I think this would be a fairly easy thing to set up considering all the assets are already made and ready, it's just a matter of setting everything up.