How useful is this? Having RPMs outside of distributions' repos is not optimal, because they won't receive updates without a repo. Generating single RPM for all RPM distributions (Fedora, Arch, openSUSE, RHEL, CentOS, etc) is also not really possible AFAIK — they have too many differences, despite using same file format for packages.

P.S. Same for deb

So as Debian user I can say that we just need the same binary we compile with cargo has doesn't have any dependence on something else so it should work everywhere.

We right now can start with the deb package and in the future we can see for a repository, a lot of projects on github release a deb/rpm package without a repository.

Publishing a package to Debian repositories seems to be troublesome: https://unix.stackexchange.com/a/620698
But that will make it propagate to its derivatives, incl. Ubuntu and its derivatives.
There's also a risk of making it into stable repositories before we reach first stable release, which will make it stay like that for the life of that Debian version.

Indeed we can think about crete our own repository in the future.
I am more right now on step 1, do the packages.