Thanks for the kind words, everyone!
I'll note, the prototypes I've done on those S-to-C FLEX-WTs are already 6 tiles long across the board, whereas all the FLEX Outside Shift ramp prototypes are 4 tiles long. I'm leaning toward the 6-tile approach, particularly since it might allow me to do some . . . interesting things . . . with the RHW-2-to-4 transitions.
To answer your question, roadgeek, pretty much any of these FLEX implementations we've created are theoretically capable of that. That's definitely true of FLEX-WT. It would indeed require quite a bit of code--somewhere in excess of FLEXFly itself, which is actually only a paltry 104,282 lines of RUL2 for FLEXFly-V2 (removing L0 RHW-2 crossing support kept that figure manageable). Figuring out a workable IID scheme would probably be the most difficult bit, and it's not anything I'd expect to see anytime soon, but it's not off the table.
There's also the fact that I suspect people are going to start requesting non-RHW under/overcrossings, which adds quite a lot to the line count--hence why those haven't been added with FLEXFly.
Jack_wilds, to answer your question about the underground view, we're pretty limited in terms of what we can do with it. By all appearances, the game has two underground views--Pipes and Subways--and that's it. I'll never say never, based on my long time doing this (indeed, who would have expected New FLUPs?), but at this juncture, I'd say it's extremely unlikely. I'll also note that both eggman121 and I experimented with Subway-based Underground Rail, and suffice to say, the game didn't like the Passenger and Freight Train transit types on the Subway network very much.
We're looking at killing all the fiddly URail crossing pieces by adding Rail paths onto the FLEX Overcrossings that New FLUPs added, but the base URail is presently out of reach for that sort of reimplementation. My attempt to do a "Dual-Network" FLEX piece setup (a la Hybrid Railway) didn't go all that well, either, as it left above ground components.
-Alex