Casting json (or jsonb) to real

I have a jsonb column which just stores a value, not an object with
key/value, e..g

"right"
"[0.563426, -0.104352, 0.819550]"
"[-1.024841, -0.235817, 0.591118]"
"1.4531"

When I know this value is a floating point value I would just like to cast

SELECT value::real but you can't do that. You can do SELECT
(jsonbcol->>'somekey')::real, but these columns just store a value.

What are my options here? This is json data, sometimes it is an array, etc,
but for certain rows I know it to be a floating point value.

--
Wells Oliver
wells(dot)oliver(at)gmail(dot)com