Type casting is fine but if you need to use schema.rb you'll have to use the sql alternative. Adding explicit support for the existing datatypes allows, amongst other things, the schema.rb
We had to abandon schema.rb early because we use PostGIS, functional indexes, partial indexes and foreign key constraints, none of which are supported. (FKs may be supported now, but at the time we had to monkeypatch AR to support it, before eventually abandoning schema.rb altogether.)
Schema.rb is inherently a broken concept anyway, because it's lossy. What you really want is the SQL, which is the only format that completely encapsulates your schema in AR. I often wish AR was declarative for that reason.
The default Rails tooling for loading and dumping the structure is also completely harebrained (google it and you will get a gazillion hits), so we wrote our own internal gem that does all of it for us, along with overriding db:test:prepare.