I wonder why the entries Piper Verlag GmbH and Piper Verlag are separated.
Piper Verlag is the name, and the GmbH is the legal form, so IMO they should be merged an the Piper Verlag GmbH should become an alias.
But I would like to ask the community for opinions.
For some good reason all these publisher entries are separated in discogs.
For merging we have to prove that it has been the same throughout the years since the publisher was founded.
It was founded as R. Piper & Co. - when was it renamed to Piper Verlag GmbH? In what time period the name “Piper Verlag” was used in publications?
So, don’t be too fast with merging publisher variants 
It’s much safer to use the relation possibilities.
Maybe I don’t get the good reason in some cases. And maybe we should wait for more entries to show up, but for the three entries at the moment:
1994 Piper Verlag
2005 Piper Verlag GmbH
2010 Piper Verlag
and all copyrights are credited to Piper Verlag GmbH.
Looking at my books I have some from 2002,2004,2006 and 2009 all credited to Piper Verlag GmbH.
I’m pretty sure, it has not been renamed from Piper Verlag to GmbH and then back. So I think this is not more than an alias in this case. But of cause more entries will make it more clear.
For sure, when renaming, merging and splitting is happening, this is the best way to solve. But here I think of an alias.
No, for sure. But I think I was not precise enough (again).
So, when we are merging these two entities and use “Piper Verlag” as alias as you propose.
Piper Verlag may have been a brand used for more than just one entity.
E.g.: Piper München Zürich, R. Piper & Co. Verlag. It may well be, that “Piper Verlag” and/or “Piper” also appears in editions of these entities.
You would have to use the same alias for diff. entities, then. And sometimes you will find older books without the legal name mentioned. Just the imprint or brand.
I think it’s better to collect more information before deciding how to deal with all these publisher variants.
I’m not sure if I get your point completely. But I understand, that we loose information if we merge identical things named differently on editions.
What we need is something like name variation, then we could combine publishers and authors which are identical and still mention how they were named.
For authors it is already planned: https://community.metabrainz.org/t/author-aliases-no-method-of-crediting-works-under-pseudonym-s/489236/2. Maybe @mr_monkey can tell us, if something similar is planned for publishers.
And at least if we don’t have a name variation, there should be a useful relation to make clear that things belong together. Otherwise, we will have a situation like on bookogs where almost each publisher has multiple entries with small difference. But in fact they often mean the same thing. E.g. the Heyne Verlag: