Well that very similar to how the Linux kernel does it. The linux kernel does it a little differently in that it uses the chacha8 stream cipher instead of a XOF. The chacha8 stream key is frequently reseeded by hashing the entropy pool with blake2b over the collected randomness from all sources but a lot comes from the nanosecond timing of hardware interrupts. Depending on configuration the blocking rng does not return unless 256 bits of trusted randomness are mixed into the entropy pool.

If anyone is interested in this topic please just read the code[0]. It has a lot of interesting tricks that you would not have just rolling your own.

[0]https://github.com/torvalds/linux/blob/master/drivers/char/r...