Vetting the cargo

> Maintaining compatibility is hard.

Don't disagree here.

> The deprecation of old crates and replacement with a new ones usually happen when the desired functionality is impossible to add in the backward-compatible way.

In my experience statements to this effect are, for the most part, little more than mumbo-jumbo that people pushing for breakage use. The reality, again in my experience, is that backwards incompatible changes occur when some developer or group thereof decides that some new way of doing things looks more "pretty" than the current way so they make the change and then substantiate it with the above. I don't rule out that the average Rust developer is honest and hard working such that whenever faced with an issue they do their utmost to attempt to not break backward compatibility and my experience does not hold, but that is counter to everything I've seen thus I'm staying sceptical.

I would also like to point out the measure for "backwards-compatibility" has to be something like:
1, The overwhelming majority of your users don't notice
2, Those who do notice, notice small things and very rarely

Otherwise we end up with the absolutist argument of "every bug may be depended upon by someone, thus *any* change (no matter how straight-forward) may break something thus we wouldn't be able to change anything thus there is no backwards compatibility thus we can change everything willy-nilly".