Trying to get larger/accessible toilets on planes via a campaign would be a complete waste of time in my opinion. If you suffer badly enough from PD symptoms to the sort of degree that requires a re-design of aircraft toilet facilities, it might be time to re-think different modes of transport and different locations for your vacations.
If on the other hand, you can adapt and plan your journey more efficiently and use the resources offered by the Airlines and Airports to better use, it might be a better option to champion a cause to enhance the existing 'special assistance' facilities.
I've used the special assistance at my local Airports for at least the last 5 years and each year their service has improved. I mainly use E***jet and I book seats as early as possible. Apart from getting a good value price, I also get refunded the additional money I paid for seats up front near the toilets. Disabled people cant have seats in row 1 (not always the best seats to have anyway because the bulkhead interferes with legroom) or seats near to other exits but its all ok from row 2 backwards.
Its fairly easy going through Airport security and Customs too. A dedicated helper will push you in a wheelchair through all the obstacles and queues that usually make our holidays a living nightmare and right up to the Aircraft door. I have diabetes as well as PD and my insulin needs to be kept chilled. That's all sorted for me (provided you inform them with plenty of notice).
As in all processes things occasionally go awry. No-one or no company can guarantee that nothing will ever go wrong but if certain things can be improved or bettered and pointed out to them in a fair and practical manner, I'm sure the Airport authorities and Airlines would try to oblige.
At the end of the day, low cost airlines are dependent on profit margins, and disabled people are valuable customers. Its in their interest to improve this service but they can only do that with input coming back to them from us.
I think this sort of campaign is a much more realistic proposition.
Failing to prepare is preparing to fail!
Btw....we say Aeroplanes in the UK, not Airplanes