I love this post, very well said and written.
if you don't mind I will add in my thoughts on points 1 and 2.
1) I don't believe it has anything to do with this decision for a few reasons. The new spur line on the Epcot beam has nothing to do with the Resort or Express beams, it's power is taken from a different source. If in the event you needed to move a work tractor between shop and Epcot, you could do so without any downtime of the resort line. Actually if they needed to move a tractor out of the way for whatever reason they could easily park between switch 8 and 9 and leave it there without even shutting express down.
2) I believe maintenance is the number one reason behind this whole thing. The trains are old, they are running far more than was ever originally planed and break down at an unacceptable level.
Speaking from experience and personal observations, shop only ever gets to take care of issues that cause major problems, usually its when a train breaks that it gets major work done, preventative maintenance is lacking.
Without getting too geeky and too into things, the trains are horrible to drive. There are constant alerts, popup messages and alarms that go off, trains will randomly stop, false ambers are common due to glitches in the mapo system and the front cabs have mold in them, sometimes you get lucky and have a working AC in the front cab.
Hopefully they will use this extra time to take care of these issues, the problems are not going away or getting better, they are actually getting worse. The trains need regular downtime and hopefully Disney can use this time to make sure that during their actual operating hours they actually operate.