The intent of the interspecies tag is for any two different humanoid species in a romantic or sexual context. In practice, it has almost always been used as a padding tag alongside bestiality or in place of bestiality. I actually gardened it massively several months ago, clearing out hundreds of mistags and still have to do weekly passes to clear out the horse porn.
But the problem is further than that. It's almost never used for its original intent: Tagging Monster Girl x Human content. The vast majority of the tag is pokemon (be it pokephilia or a pikachu and an eevee fuckin'), more recent furries, and goblin rape. Very, very few people want to tag lamia x human pics with its own special tag.
With the various furry with X tags, the recent pokephilia tag creation, and how on many other boorus it is used in place of bestiality, I really wonder about the viability of the tag.
Should it be nuked? Deprecated? Should we manually mass garden ~monster_girl ~monster_boy sex?