Look at New FantasyLand, Look at Avatar.
Disney showed us pictures and videos of Avatar in October of 2013 and Land is expected to open in 2017.
So if they show show concept art of Star Wars Land at Disney Expo in August 2015...be prepared for Star Wars land to open in 2019. A long long long time from now.
I realize Disney doesn't move fast, but there is a BIG point to keep in mind here. James Cameron is a perfectionist to his own ideas and Disney does NOT own any of it. Thus great debates with him have dragged a normally lengthy design time into what it is now.
Disney now owns Star Wars and had talked prior with Lucas on other options, so they have Imagineers already experienced with the franchise that they now OWN.
After all, James Cameron doesn't mind sitting in a sub the size of a bath tub for 3 hours to see how unique the sand is at the bottom of the ocean. So he sure doesn't give a <insert word of choice> about how long you wait to see his perfect dream nor how long you will wait in the hot Florida humidity or rain to see his masterpiece. I can ensure you there has been a lot of delay in the design phase that will not occur for Star Wars. In fact, I'd bet that with Star Wars and Raiders as Disney owned properties, the Avatar connection is quietly being locked to a minimum so they can round out AK and kick off a larger DHS effort of SW, Indy, & increase the Pixar presence.
However, with theoretical expansions at DL and DHS, there are a few variables that could lengthen the time:...
DAK with Avatar being in a corner of the park that could be closed off, doesn't have the same issues. Though even there some extension of the timeframe may have been caused by the need to build the new FOTLK theater before shutting down CMM.
I think your points are the only real delays in getting Star Wars built and running. Iger isn't stupid and with Star Wars and the fan base, Disney will have the ability of HP to wave a wand and print his own currency. They want it yesterday, but there are simple annual budget restrictions as well as what you point out, infrastructure.
None of us know the size they are planning. I would bet it will be comparable to Carsland in that Disney can add a lot of space (sorry for the pun) to spread it out, theme it well, and leave a few future pad locations. I am sure they will be moving, demolishing, and more. I wouldn't be surprised if other work was done at DHS in a fashion comparable to the great California Adventure over haul.