Let's talk about version 3 first. Don't take this the wrong way because any idea deserves consideration, but IMO, version 3 belongs on a scrap heap. The main problem is that your outer oval runs through 2 double-slip switches, a recipe for disaster. Double slip switches should only be used (for model purposes) when you are constructing a yard or terminal; in other words, where only slow speeds are allowed. Running a full speed passenger or freight train through them creates just a "YIKES" moment.
I like that you've moved the yard to the center, but instead of connecting it to the mainline, why not connect it to the inside most passing siding. That way, the passing siding can also double as a yard lead, allowing you to "work" the yard without fouling the mainline.
Version 2.1 is a definite improvement over earlier versions IMO.
Finally, you mentioned the idea of an around-the-walls layout. Generally speaking, that means no part of the layout is more than 30"-36" away from the wall supporting it, requiring no duck-unders to reach any part of the layout. That method also usually requires some sort of bridge or moveable section of benchwork right where the entry door is located. Based on the plan you started with, you could place 2 reversing double track loops (I like to think of them as "bulbs") in the southwest and southeast corners of your room (leaving enough room for access) that then connect to a yard / town along the top. Some people actually put the reversing loops over each other in one corner, place a yard and engine house in the other corner, and then use a rise (or fall, depending on direction) in the two rear tracks of a 4-track mainline along the north wall.
I hope this makes some sense and doesn't overwhelm you!
Chuck
