because you worked hard on this set up

with the lore so far( at least tv show wise) one bending type only . case in point none of Aangs kids had more then one element and one of them was even a non bender, with having 2 very high level benders for parents if any one was going to get something over the top i would think that's where it would show up.

I -think- that only the Avatar would be able to learn multiple styles of bending. Toph's metal bending is really just her bending the impurites of the metal, not the actual metal itself. Now, I'm not sure, but I think it's a 50/50 chance that the kid will either be a fire or water bender. I'm not sure I could be waaaaay out in left field with this. Just going off the top of my head.

well following that line snow,blood and, plants( the swamp tribe) are all water bending.

lava and metal are still earth however lava bending i dont think has been done at least in the show( final battle with Phoenix lord might have some stuff pass for lava not sure its been a while for me)

fire,lighting and, combustion are all still fire but combustion was only that one insane assassin experiment guy but he started as a fire bender if i remember right.

that just leaves air, and sound which on some level i don't know if you can define something as sound bending instead of just high frequency air bending

ps that weird i can heal stuff only some water benders can do might be a cross over of water/spirit but that would break this

yep shits weird when you go off cannon huh?

Not unless the child is the avatar

You mean Ron Swanson is the Batman of civilians.