Note that rust-crypto is no longer maintained. (though RustCrypto project aims to supersede it) So it will be better to start such project as a separate crate in the same fashion as rpaillier.
@manishkk: Sorry for the late response, but currently I haven't much time for open source development or community work . I don't know your crypto background, but Paillier crypto system doesn't seem to be uses very often in real world applications (at least it was not as I worked on my projects). From your main post I assume that you are interested in similar (privacy preserving) algorithms like I worked on and which were the reason for me to develop jpaillier and rpaillier. During the work on my Master thesis I saw a lot of research work on other such algorithms. So I would suggest to use Paillier only as a starting point, because it's not to hard to understand (at least it wasn't for me - and I'm by no means a mathematician). For me working on it also was a good starting point to learn more about cryptographically secure implementations, side channel attacks and such stuff, but keep in mind, that my implementations of Paillier are not hardened against such attacks. If you still want to do something with Paillier, there is a second use case described in Paillier's paper - using it to create digital signatures, if I remember correctly. Maybe you are interested in implementing this.