the MAJOR benefit of a larger sump volume
is not the "whopping 250cc" difference,
or even the 946.352946 cc difference of some after-market pans,
and will NOT be realized in either case if the increased volume is filled up with more oil.
Any advantage that might be provided by a greater quantity of oil
PALES in comparison
to the fact that a horizontally opposed twin,
by virtue of it's large displacement and the design of BOTH pistons moving inward and then outward simultaneously,
generates SIGNIFICANT and UNDUE pressure differentials within the crankcase (esp. at upper RPMs) ...
and engine performance / efficiency suffers as a result.
A larger (and unfilled) sump volume
increases crankcase air volume.
That additional air volume reduces pumping losses for the engine,
and the lower crankcase pressure reduces blowby
to result in a more efficient engine.
This will be the reasoning behind BMWs changes.
A revised pick-up & extension would not even be a production consideration
if the deep sump weren't a part of that plan.
The 1976 R90S Superbike generated SO MUCH crankcase pressure –
that the resulting force was known to blow it's cylinders apart from the case !!!
And a practical note:
Cranckase pressure is the reason that so many Type-247s are prone to weep oil at the cylinder base ...
and foul the right carb of early models with oil.