The article mentions that none of them exhibit wear marks that are characteristic of tools.

Do you think show pieces in rich households would be used?

I’d argue if they did, someone was getting fired immediately.

Have we found any other shows pieces for other household items? Because if not, it’s very unlikely that’s the case

Yes, all the time. Like silverware, ornamental swords/weapons like axes, jewelry.

I’ve seen many vases and other such vessels in the homes of rich people that are not used to store liquids, but instead sit there empty on a console table in the hallway!

In that case this isn't a tool, it's a decoration. And if none of them are worn, then the decoration isn't imitating a knitting tool, since some would show wear if that were its actual use.

Would the royal household also have decorative brass stone masons' chisels, carpenters' planes, doctors' scalpels, and farmers' sickles?

I don't really buy that theory. Do we have any other examples of fancy decorative versions of working class tools?

Anecdotally, I have seen decorative plates hanging on walls, spinning wheels, ships wheels, oil lamps, etc all used decoratively in contemporary settings.