As pilotwolf says, there's a lot of difference between the light aircraft avionics and the airliner. If you have interference from something local to the light aircraft on a VOR or a DME channel and you're not using VOR or DME, you don't have a problem. If someone in the back of an airliner has a machine that's causing a problem, how do you know when you're up front what is causing it?
Controlling multi system EMC is a difficulty, and adding factors that are unknown, even if unlikely to cause problems, isn't a good idea.
So, sorry, paulo, as someone who has been making a living out of radio engineering for over 40 years and doing EMC work for 15, I'm in favour of maintaining the ban.
The use of WLANs on board could be interesting if for some reason the clear channel assessment didn't function correctly and a 5GHz one transmitted in the middle of the MLS band. Although I believe that MLS is effectively dead in the US and isn't that widely used in Europe as yet - if it ever will be, since differential GPS or Galileo will do a cheaper job as far as the airport authorities are concerned.