Hi!
transformation to WGS84. Some places like important peaks or astronomy observatories can be located with such precision.
True, but this probably won't be kept up-to-date and most likely would be useless for Wikidata users since random very precise data can not be relied on unless there's a guarantee certain set of data (e.g. all observatories) have the same accuracy and it is kept up-to-date. Which Wikidata does not have.
So I am generally against limiting the number of digits too much, but limit it to something like millimeter precision sounds reasonable.
I think we should at least limit it to specified precision (not the case today) but maybe even more in case precision is too high. I don't think anything beyond 1m is really useful - please provide use cases if you think otherwise.
Also, wikibase:geoPrecision seems to be completely useless in the form it exists now. Is anybody actually using this value, and if so, how? If not, I'll probably change how it works.