Well both Spanish slot car manufacturers already have adapters of sorts. The SCX Classic and Scaley Classic are the same and going from SCX classic to SCX digital is possible with some of their own adapters. Yes that would mean you have two single straights (Scaely Sport /Scaley Classic adapter to SCX Classic/Digital) but it would work.
Ninco also has a "chicane/squeeze" that hooks up to with Scaley Classic and therefore by extension, Sport. Again you would have to go Scaley Sport/Classic to Ninco.
FInally I own a Cartronic to Scaley Classic adapter. It was a total fluke on fleabay and I have not seen them again ever since. Cartronic was created by a former CEO of Carrera so they are about the same as the old Carrera Profi system. Slightly less wide than their Evolution/Exclusiv and with a different tab system. I have actually incorperated some Cartonic track into a Scaley set up well.
So from my point of view the only thing missing is a direct Sport to other system adapter and and adapter to the modern Carrera system...
Having said that... like I said, I have tested a Cartronic/Sport mix. The Cartronic track is very similar to Carrera. There was a very marked reduction in both grip and magnetic downforce. I presume that with modern Carrera track it would be the same. It was fine for straights and banked curves but a little chicane was very loose.
I plan on making my own adapters to be honest. I can't see any manufacturer doing it for a few reasons. One is compeltely practical: The radii and lengths of peices of track are completely different. Unless you are careful, the track won't match up. There are also intelectual property and copyright issues. Also they are opening themselves up to a slew of problems because track behaves very differently.
Since I do run the occasional 1/24 car I am planning on making my one "direct to Sport" adapters using the "side swipe" track and bit of Carrera Profi track. I plan on soldering the track together (using wire from underneath) as well as using conductive self-adhesive copper tape on top. The "Profi" track is actually wider than the current Carrera track if you make it 4-lane. :-)
There are Cartonic/Carrera Profi adapters, so while I could go Sport/Classic -> Classic/Cartronic -> Cartronic/Profi I think that is getting slightl yout of hand ;-)
So the bottom line is there are options for most there and the ones that are missing are so different I don't think it really viable... my .02€