I don't think that I would want a unpressurized cooling system on my 990 ADV.
When pressure increases, boiling point decreases and visa-versa.
By eliminating the pressure aspect of the cooling system you are reducing it's ability to perforn under the most harsh of conditions.
Now add in a high altitude enviroment and this will further reduce the boilover temperature.
A no-pressure system might work on static machine with very efficient radiators & cooling fans, but on a water cooled bike at slow speed I don't think that it would work well.