This sounds to me like the exact opposite of what I want as a user. More specifically, Rust provides stability guaranties that are vital to many users. Those users rely on the stable interfaces of the various tools and of the language specification (as much as it was specified thus far).
Yes, competition is healthy and should be allowed, but a requirement to be open about it is just fair and allows the users clarity with regards to what exactly they are using. The user (especially in the case of a programming language) is fully able to judge and compare alternative implementations and alternative languages by their merits. On the other hand, allowing forks to masquerade as the original is a known evil corporate strategy (called EEE) to stifle competition and very much anti free software.
as a side note, People keep conflating "Rust the language" and "rustc the compiler" in these kinds of discussions, even prominent rust community members. I'd be very concerned to read that the Debian project has forked "Rust" (the language?!) for example. however, I'll be totally fine if they forked the compiler or its packaging. This is in the same vain of clarity of intent and of communication with the users.
The trademark debate should be very clear about this point - The trademark should protect "Rust the language" in order to make the compiler really free software.
Last point, regarding the complaint about Cargo's integration with rustc invocations - I'll look at what there is in C++ land as a good starting point, i.e. we should be able to support different compiler implementations & vendors of the language and as a user I should be able to specify which implementation I prefer to use by e.g. setting a common environment variable. This is a worthwhile enhancement to have instead of having different forks having the same name.