@Noqanky:
Wait, why do things need to be in trios again?
Because the tumblr indicated it was and the type it mentioned made no sense.
And any new element needs a rock/paper/scissors balance to it, otherwise it ends up broken (dragon and psychic types originally)… or useless.
To those of you saying no, why not? Even if you argue that it's too late into the series, I say bollocks … we have Nintendo franchises that are more than ten years older than Pokemon. So what if people are already used to a specific set up?
I'm all for a new type. I'm up for a dozen new types, or a complete rebalancing in how things work. Its just at this point, they've been implementing a system for 15 years across dozens of games (not just the main games) and it seems too late to shake up that particular aspect of the series. (But poison could hurt more things, grass weak to less, ice get some defenses, split water into multiple types, etc. There's definitely room for balancing yet.)
You can point to the physical/special split as a major change, and it was… but it also made sense and gave nearly everything way more versatility and balance. (The only hindrance was things that had a high special or physical stat that relied on certain moves, but that didn't happen too much.)
but not as much as shaking up the multi tiered rock/paper/scissors structure they have going. Still, there's plenty of space to make old elements better, I wouldn't be against a new thing at all if it gave a new offense or defense to old things, or mixed up a couple of older type monsters in some way.
@KaizokuJinbei:
They can always add the type in Magnamite for example was just electric in Gen 1 but steel was introduced in gen 2 and was added as a second type.
That was ONE monster. After ONE generation of balancing… and it super benefited from defensive steel typing.
Adding a type now would affect and change a lot of creatures, giving them weaknesses they didn't have before (and strengths) People would adjust to the new thing of course, but it would change a lot of old things... usually when they want to fix a monster in regards to stats, type, or massively tweaked moveset, they just give it an evolution instead.