John, this was also true of nearby Liège and indeed a big part of what is now French-speaking and Dutch-speaking Belgium and what is now France? Doesn't your reasoning imply that we need to make some very awkward changes? Nearby Liège is Lüttich in German, but some of the German names for places in the large Lotharingian region, which is mainly NOT German speaking, are hardly known anymore.
Put it another way, there was no official language of the Holy Roman Empire. (Unless it was Latin?) It certainly wasn't modern German.
Remember we are talking about a single letter of spelling difference, so compared to the range of spelling variations at the time, this is nothing.
I have to say I was not expecting any opposition to this proposal because it seemed simple. As far as I can understand Wikitree habits and policies, this is according to them? I have never seen anyone claim that any place in the Holy Roman Empire should have German placenames, and I have never seen anyone on Wikitree argue that a Germanic etymology is enough to make a place German speaking. (Note the big difference between the words Germanic and German.) Such new policies would mean a lot of strange changes would be needed.
Limbourg is French speaking, and modern English, Dutch and German speakers generally therefore spell it Limbourg, if they know the place. It has been spelled many ways, but it has certainly been Romance speaking for a long time, possibly since it was founded. It will never have been soully Germanic speaking even if it will always have had speakers of various dialects of what we would now call German and Dutch. It has a generally Germanic etymology, but no one is even confident of what it is, let alone which dialect it comes from. Kupper thinks the name was chosen for its political associations. If we have to use etymology to make these decisions, then for example consider all the Anglo Saxon placenames in Normandy, or the Welsh names in England.