Much too easy to make memory errors
The counter-argument is that Rust, in order to be able to determine memory safety statically, makes it sufficiently harder for average developers to use it correctly that they immediately resort to "unsafe". I only have anecdotal evidence of that - the number of "how do I do that in Rust" discussions that seem to recur on StackOverlow and the like without reaching a conclusion and the extent to which proponents of Rust lament the way people fail to properly understand it and approach it with the right mindset: an appeal to true belief is always a warning sign in my experience.
I also fear there's simply too much of it - apart from the language itself with its pointlessly "improved" syntax, there's the build system, the packaging system and, of course, the macro system. It's a lot to learn - and most of it adds no significant obvious value. The language is also going to have to co-exist for some considerable time with others. If it appears in the Linux kernel it's still mostly be going to be working with data structures whose lifetime is controlled externally and so beyond the reach of static analysis.
I'm happy to be proved wrong, but I'm afraid I start from a position of skepticism.
Edit: BTW, I see that posts are still inexplicably being moderated. Assuming the moderator permits, I'd just like to say cheerio to fellow commentards who have been incredibly informative and (mostly) good-humoured over the last 10 years. I've greatly benefited from your wisdom and will still occasionally visit, but I'm afraid the lack of spontaneity means participation has become unnecessarily tedious.