While I understand and perhaps even agree with the semantic argument, the reality of the web is that this will be abused. A sane implementation for a browser would be for an action button with method="get" to get basically all of the affordances a normal link has, e.g. middle click, context menu actions. Sites already exist that hide navigation behind non-links. Now they need to write JS to make that happen, which is at least a bit of a deterrent.
The proposal actually fully treats this as desirable:
> When web authors style links to look like buttons, they inherit the responsibility to make links behave like buttons in all possible contexts.
No, they don't. A web author that works to disable core functionality for links should be fired into the sun, not given easier tools to do so. If your action is really just a navigation, then the user should have the ability to treat it as such.
The proposal actually fully treats this as desirable:
> When web authors style links to look like buttons, they inherit the responsibility to make links behave like buttons in all possible contexts.
No, they don't. A web author that works to disable core functionality for links should be fired into the sun, not given easier tools to do so. If your action is really just a navigation, then the user should have the ability to treat it as such.