I think it would necessarily cause the "page to load much slower than normal" . If the secondary entry points were just a button, then it wouldn't preload additional iFrames so there would be close to zero overhead on load time. It's just basically a radio box selecting different options from a goodie box.
My personal feeling about this is that it is something that is better suited to the platform rather than the code itself, Especially when the variants contain completely different assets. It would be faster to split then, but that's just my opinion.
I think if the feature was added (which I don't think it will be( , and even if it was useless for most people (which it probably will be) , it would still have zero impact on the speed or functionality of other pages.