Considering Postgres is the first relational database to support jsonb, portability (which is the main benefit of drivers) doesn't really apply. Any decent driver or framework should let you write native psql commands, so you should be able to start using this as soon as it's released.
Being able to use Jsonb through a framework and fully utilize it (through it) are not the same things. I will be definitely use it soon, but unless it's fully supported in frameworks (...) it won't be widely accepted.
There are ORMs like SQLAlchemy (Python) and Sequel (Ruby) which try to expose as much as possible of the features of all supported databases. It is common for Sequel to add support for new PostgreSQL features while the new PostgreSQL version is still in beta testing.
What's involved in supporting JSONB in Rails? Given that you probably want access to the entire JSON blob at the Rails level, aren't you good to go already?
Sure, but it's also nice to have a layer of abstraction over psql. I personally really enjoy working with Django's ORM, for example, over writing native queries.
