Premature? No people have been complaining (or just getting very confused) about Clojure's numeric performance without oodles of invasive type-hinting for two years now.
More importantly with these changes it's now possible to reimplement Clojure's core datastructures in Clojure without sacrificing performance.
The majority of people who care about BigInts are solving Project Euler problems, not writing Clojure libraries or deploying apps into production.
The situations that deal with numbers that large are usually a bit nuanced. (i.e., "it's 1 in 2^63 of the time that I need bignums for day-to-day programming"). I agree that losing accuracy needlessly sucks (and I've been burned by floating-point), but 64 bit ints are usually good enough.
More importantly with these changes it's now possible to reimplement Clojure's core datastructures in Clojure without sacrificing performance.
The majority of people who care about BigInts are solving Project Euler problems, not writing Clojure libraries or deploying apps into production.