Yes, this is indeed something I would like to add in the future. While adding different radix kernels support for small prime factors is not that hard, writing

Yes, this is indeed something I would like to add in the future. While adding different radix kernels support for small prime factors is not that hard, writing efficient scheduler is a much more challenging task (each sequence, even for power of 2 now is split differently targeting different architectures to optimize performance). The Bluestein's algorithm typically used for arbitrary prime sizes requires both zero-padding and convolutions support which are already efficiently implemented, so it is also not completely out of reach.