A couple of weeks have passed, so I'll go ahead and answer this. The NU Viability Rankings was recently updated to have the new drops, and Alolan Raichu at the time of this post is B rank on the NU VR. Alolan Raichu is useable on Electric Terrain teams, but outside of Electric Terrain, Alolan Raichu is outclassed by other Electric-types in the tier.
On paper, Alolan Raichu has some things going for it. Being slightly stronger than Kantonian Raichu, having Nasty Plot, having a nice secondary STAB, and coverage options such as Grass Knot, Focus Blast, Surf, Tera Blast, and Draining Kiss to an extent. However, in practice, there are things that make Alolan Raichu not as good. The Dark-types in the tier such as Hisuian Qwilfish, Grimmsnarl, and Cacturne give this mouse a hard time. Even on Electric Terrain, Alolan Raichu no longer having the powerful Rising Voltage in Electric Terrain is a huge blow for it. Outside of Electric Terrain, Alolan Raichu is outclassed by other Electric-types, mainly being Jolteon and Eelektross.
Jolteon outclasses it with its Volt Absorb and is naturally faster, while Eelektross has that cool Levitate ability and has more bulk.
Source
The statement above sums up what makes Alolan Raichu outclassed outside of Electric Terrains. Without Electric Terrain active, Alolan Raichu is slower than Jolteon. Jolteon can utilize Calm Mind sets to make it a scary breaker, especially with Tera. Jolteon also has Volt Absorb, allowing to to come in on Electric attacks and restore some HP. Jolteon being faster allow it to be a much more effective Volt Switch pivot than Alolan Raichu.
Eelektross also outclasses Alolan Raichu, but this is bulk wise. Eelektross also has Levitate, meaning it switch into Sandconda more easily. Despite having lower speed, Eelektross' bulk and lower speed allow it to be a good pivot since it can utilize a slow U-turn to bring in teammates.
I might as well mention that as a Psychic-type, Mesprit exists, and Mesprit being versatile makes Alolan Raichu outclassed as a Psychic-type.
TL;DR Alolan Raichu is useable on Electric Terrain teams due to its speed being doubled during Electric Terrain and having useful coverage moves. However, outside of Electric Terrain, Alolan Raichu is outclassed as an Electric-type, with Jolteon having faster speed than Alolan Raichu, and Eelektross having more bulk than Alolan Raichu. These two Electric-types also have useful Abilities in Volt Absorb and Levitate respectively.
