I have had several thoughts about Walts plane. It has survived about 3 changes in company top management and the rules have changed with each turn-a-round. And with each turn, the top brass have become more hardened in park/resort decisions.
the The plane was actually a company plan, true it has been branded as Walts plane and with the guests that holds incredible value. It was the first change of leadership, which was still closely tied with Walts memory that decided to stop using the Mouse and park it. It would be interesting to find a story involving the reason they decided to stop using it as an aircraft needs to be used or it will deteriorate in the weather. Perhaps the memory/attachment to Walt was enough to park it. Walt passed about 6 years before WDW opened. I have not read anything about the Mouse in that time period so it may have been parked at that time but I would reason that Roy would have used it. Mouse was used by everyone that needed to travel so it seems odd that its use was just ended.
The parks are struggling with space, the attractions are not holding the guests attention. The best way to preserve it would to park it inside a large building, perhaps a dead sound stage and open it to guests as a themed attraction ( The Walt Disney Story, and all the artifacts that go with it comes to mind ). It is just a very big cumbersome item That was Walts, and yes that holds tons of memories of Walt by the guests. However, this third group in charge do not impress with the way the parks just sit and lose appeal as they do. If they held the interest or even had more of a mindset to operate/maintain the parks as Walt did, I suspect the parks would be in much better shape. The operating agenda seems to be to build the attraction, open it and let it run until it needs a tweek. This is about the condition of Epcot and DisneyMGM. MK would have befallen this curse but with the addition of attractions built in open areas in the MK over the years it has retained it's interest. But the original land layout for MK is about used up. Expanding outside that original area will get expensive so look for more attractions to be demo'd.
BUT Mouse isn't going to improve, it won't change. It holds Walts memory, a link to guests minds and it needs to be tied to Walt through at attraction or as mentioned perhaps the Walt Disney Story. Back Lot is gone which is why Mouse is coming up in the forums. This could be a good scavenger hunt -- Find the MOUSE.
... That said... and realizing the followers of Walts magic would like to see the mouse end up in a museum like atmosphere to be pampered for as long as the parks exist.