I just think it's a good forward-looking idea to consider building the infrastructure to support other altcoins. I think there would be a small demand now, but who's to say there won't be in the future. There was a time when crypto exchanges didn't want to list coins beyond Bitcoin and Ethereum, and there was a time when mining farms wouldn't consider anything besides Bitcoin. Obviously that has all changed now, and I'd argue that some of the services that came out on top probably were early movers into listing altcoins on their exchange or buying the right miners and configuring their software to handle those altcoins.
It's very easy to see that in 2030, there might be a large demand for mixing altcoins. Why not branch out and start building that now so that the service is ready when the demand comes?
First you have to make sure the protocols being used in the altcoins actually allow for obfuscating outputs.
Ethereum is obviously so, because Tornado Cash was so good (that it was sanctioned). Dogecoin and Litecoin are similar to Bitcoin's network so they could work with little modification. And that's about it I believe.
Most other stuff that is "pegged" to some blockchain cannot be hidden effectively because it's attached to other addresses and also in many cases the tokens can just be blacklisted by the central authority.