Just my .02 cents here.
For 'pure distance' very few casts can/could beat the single spey. If you watch the 'best of the best' 90+ of them are using this, or a very similar cast as the fellows (and Ladies) are using long belly lines.
That said, there is a minor 'revolution' going on as some casters are now using very short head lines (Skagit and Scandi) and they can really rip these things. When these lines first entered 'competition,' it/they caused quite a bit of 'controversy.' (Think the the first was a few years back in San Francisco.)
Are they 'real fly lines?' 'Should they be allowed in competition?' Etc. End game, at least with some competitions (can't speak for all) was: "Yes." The short headed lines were used by thousands of fishermen around the world. Commercially sold to anyone with $70.00 (give or take).
Will they take over as the line of choice? Rather doubt it.