> I tend to use proprietary relicensing and Open Core somewhat interchangeably because they typically have the same outcome.
That's debatable. In any case, 'open core' and 'dual licensing' are very different in terms of what they actually are, regardless of their outcome.
Anyhow, ignoring the terms we use, Canonical appears to support giving the option to purchase a non-FOSS license for FOSS code. There are upsides and downsides here. Like RMS, I tend to not see a huge problem, it depends on the situation.
Were Canonical going to, instead, start selling proprietary code, I (and RMS) would strongly disapprove.