The same problem also applies to the M series but those take care some of the problems in software.
.. and microlens design.
Mechanical adapters don't influence optics, but they can affect alignment. That is not really a big problem in many cases as you often only have a central point of focus, but an excessive tilt of the lens would cause problems.
cause problems - with an excessive weight hanging off the end of the adapter. Unless you support the camera/lens under the lens for hand held shooting or, preferably, a tripod mounting foot on the lens or adapter.
Bottom line: legacy lenses >= 50mm are, on the whole, more than usable with an adapter. Sony have, approximately, 15 lenses planned for the Alpha over the next 18 months - those wide angles need to be stellar.
If, on the other hand, you're thinking of buying an A7 to hang a 1kg Zeiss Otus, via an adapter, off the diminutive Alpha - then I would suggest that misalignment problems aren't the core issue you're facing ... ! [Light hearted quip - not directed at you, Erik]
On a more serious note, one thing I have yet to see any reports or comments on, is the 'adaptability' of the Alpha with tilt-shift lenses.