You want to go after the Electric-type now? Only super-effective against two types - Water and Flying. Resisted by three types - Grass, Electric and Dragon. Only has three resistances - Electric, Flying and Steel. It is ineffective against Ground-types too. Just one vaguely powerful current generation power-creep legendary Electric-type and it's already on the chopping block?
I look at the context of the electric moves in actual battle, and how players actually use them. Electric is powerful in practice, regardless of hitting only 2 types super effectively - and was already so even before Tapu Koko.
For one, there is the notorious "Bolt-Beam" Combination. Pairing Electric and Ice moves is so good for neutral coverage that many players now have opted to use it as a Pokemon's only offensive moves - even when the Pokemon themselves are neither Ice nor Electric!
Also, for some reason, there is a strategy revolving around Porygon-Z called Z-Conversion. It allows Porygon-Z to switch its type with move it has of your choice, and raise all its stats at once to sweep teams. The most common choices? Ghost or Electric. I don't think either one is a coincidence - even though both only hit 2 types super-effectively.
Thus, if Ice types resisted electric (1/2 damage), and lost its Rock weakness, I see many good things happening:
-Ice types can actually switch in more effectively, as stealth rock only does neutral damage.
-Players will be a little more weary about using Bolt-Beam, as Ice types will then actually switch into this strategy.
-Many Water/Ice types - Particularly the bulkier ones from the lowest of the low tiers - will see better play. They'll be able to hold off stealth rock damage, and only grass and fighting hit super effectively. They were screaming for a buff, and this would be a reasonable one in my eyes.