Germanic lineage arrived from the east?

[Jaska]

Alanarchae:

I agree it has a basic root. Often placed as the or one of the earliest post-Tocharian branches. Almost certainly rooted in CW variants that settled initially somewhere between Denmark and the east Baltic. However, I suspect that what existed in say 2800-1600BC might have been a bunch of similar but drifted dialects that might have formed from the early PIE-Germanic branching point.So once you start to see admixing in the genetics you might also have seen admixing of a number of related dialects all of which were ultimately rooted in the same branching off point from PIE. The dialects may have been subject to both drift and differing substrate effects. Once they were intermixing and involved in the Nordic Brinze Age network it could have been quite complex imo.

I am not sure are we talking about the same thing here...
As I explained, languages or dialects do not admix like ancestries or cultures do. When speakers of other dialects arrive, usually one dialect prevails and other speakers, or at least their children, adopt that one. Of course some contact-induced features can spread, but that does not change the dialects or their status or development history. Historical phonology can tell us the development of different languages and dialects, and all Indo-European branches are clearly different from each other. 

"Drift" is therefore essential part in linguistic diversification, and it occurs always after a while, when speech communities get separated. Substrate, superstrate or adstrate influence can also occur, but they cannot level down the "drift" development of a language. Shared features and differentiating features of language co-exist together but independently from each other.