It wouldn't have to be deemed a punishment, merely a procedural item as part of establishing the Republic of Britain and eradicating any trace of royal privilege.

> Technically just abolishing the monarchy / taking away their powers would suffice.

It wouldn't suffice, because they still derive a great deal of power from their inherited wealth. What's the point of abolishing the monarchy if we permit them to remain as landlords for huge swathes of the country? Then they're still lording it over people economically, even if no longer doing so constitutionally.