Rearward weight shift due to acceleration, while true in theory, would happen after you accelerated, or started to accelerate. So, that meant you already had traction. If you are getting additional traction due to rearward weight shift, almost by definition, you don't need it. Accelerating slowly (like when you are on snow) won't produce any significant weight transfer, IMO.

The weight shift that does matter is while climbing a hill, at least if you are going forward. The best traction of all in that situation is a front wheel drive car, backing up a hill.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
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2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue