Yeah, I really wish Ash finally gets those types which he doesn't have so far. But I really doubt that the writers will break the trend of Pikachu being Ash's only Electric type Pokemon.
I don't see any reason why Ash couldn't get another Electric type especially since in Vikavol's case, the Electric typing is it's secondary typing while it's primary typing is Bug, so while it may have 1 Electric type move and even use the Electric type Z-move they could still focus on it's Bug typing.
Plus it would be nice to see as it could use an Electric type move that Pikachu will most likely never use. Also as for doubting that the writers would break that fan-made pattern, that's pretty much the exact same thing about the other fan-made patterns and that didn't stop them from breaking.
In all reality the only people that probably care about Pikachu staying the only Electric type on Ash's teams would be the fans that came up with that fan-made pattern, in all reality Ash having Pikachu would most likely not stop Ash from getting another Electric type.
Look speculating on what Pokémon Ash could have using some patterns is nice and all but I really which some people in here would stop acting like the fan-made patterns are somehow the be-all and end all to what happens in the show and what Pokémon Ash gets.