Just from the very very limited knowledge I have of material science, a solid aluminum axle is still softer than a standard thickness steel axle. Now, without getting into a lot of detail suffice to say that unless the track is a no bite track, loose dirt, where you're running treads and QRC style driving, an Aluminum axle is just too soft. At least from my very limited knowledge, and I could be wrong. But, I'd like to see hard numbers, and I don't know where to find them if they're out there.
Now, I'm not talking near failure, as NONE of the axles will ever be remotely close to failure at any point, so that's not even a consideration. It's all about handling.
For example he's looking at going to a thicker steel axle.
A thin wall kart axle is around .125 or an 1/8.
Standard axles are about .1875 or 3/16. A LOT of standard axles are .190 thickness.
Thick wall Axles are .250 or 1/4.
They don't mention the year of the Excentrik, but even the 10-11 are fairly stiff in the rear. My personal opinion from experience with an Excentrik, especially 12-13 models are very stiff, so when looking at things from a handling perspective, unless they're trying to "Fix" an issue, the standard axle is sort of the Goldie locks of axles. It's just stiff enough, but will degrade over the season if it's run hard on higher bite tracks. But, offers enough flex to still hook up on lower bite tracks too. So while a thick wall axle might not be a bad idea, it could potentially hurt on lower bite tracks, potentially to a point that it just will be very hard to ever get enough drive. I struggled with this a lot even with a standard thickness axle. So I opted to stick with the standard axle. If they choose to go with a thick wall axle I won't say it will be a bad idea.