I’m personally not a fan of elastic tabstops, primarily because they significantly increase the cost of laying out text: it changes the problem from a local, per-line one, into a global problem: a modification on one line can change how every line in the buffer is rendered.
Although I haven’t used any software that supports elastic tabstops, I suspect that in the real world, they aren’t as handy as they seem: because layout is now global, a very long variable name in once function can introduce excessive whitespace in every other function in the file (i.e., blocks will be aligned with other blocks hundreds of lines away).
The primary problem elastic tabstops solve is preserving vertical alignment of neighboring blocks of text. I believe this would be better solved by the editor doing so explicitly, inserting normal whitespace as required.