Why is it any better than a slow true random seed and pseudorandom numbers based on a secure hash function? I can't think of any application.

This is basically what the Infinite Noise[1] project does.

Speed is limited by the speed of a gain stage and a comparator, and can run in excess of 100 Mbit/second per second with high performance components. Cheap solutions with CMOS quad op-amps can run at 8Mbit/second.

This implementation uses Keccak-1600 with cryptographically secure reseeding of more than 400 bits of entropy at a time, overcoming a trickle in/out problem present in the GNU/Linux /dev/random system. Users who need many megabytes per second of data for use in cryptography can set the outputMultiplier as high as they like, which causes Keccak to generate outputMultiplier*256 bits per reseeding by the Infinite Noise TRNG.

[1]: https://github.com/waywardgeek/infnoise