I'm not saying that 20K didn't need work or taken out. I just find it incredibly far fetched to think that this was the grand plan. Like I said, having to wait 17 years for a replacement isn't really a plan. You can try and concoct a theory about why it took so long....but it doesn't make it true.
Here's the big picture: In late 60s the MK was planned to include new versions of all the big E-ticket of DL, excluding POTC, but including the Submarine Voyage. Flash forward, 20K was a slow loader and was costly. Disney took it out with no immediate replacement. Ideas came and went with no project moving beyond blue sky. They still didn't even really touch the lagoon for 10 years. Finally, in 2004 they tore out the lagoon, built PPS but still without a solid plan for the area. Five years later (NOW), Lasseter and other people in the company notice how horrible the MK's capacity is, how it's been 17+ years since the last E-ticket was added, and how the MK has some of the worst FL and TT aesthetics of any DL-style park in the chain. Lasseter, Iger and others get a plan put together to redo FL, going over the objections of TDO and even P&R. It includes a firm replacement for 20K, TLM. The plan is leaked and people get excited but wonder why it took so long. That's the big picture.
..And how in god's name do you know what is going on for the 50th? Our insiders aren't even sure what's definitely going to happen for the 40th!