Earlier quoted context omitted.
What's the highest offer for it that you've rejected? That seems like a fair lower bound. (Not that I necessarily support a Georgist tax in this case, since it seems that your interest in the domain is noncommercial in nature)
Wouldn't that allow random people to increase your tax on domains you obviously don't want to sell ? E.g. if you owned and actively used greyface-.com and I'd make an offer of 10 000$ just for the fun of it, either you literally give up your name (I eat the cost but that's a risk I could want to take) or you're stuck with a percent of that to pay every month/year even as nothing else changed for you.
If you're willing to pay $10000 for it, even if only out of spite, then it's worth that much yeah. The domain is suddenly in more demand than it was, taking it out of circulation is a bigger imposition on society than it was before, so isn't it right that the tax on that goes up?