There are 2 new studys from Germany which got leaked about 1-1,5 weeks ago, one from the organization of the e-cigarette merchants (sorry for that translation, since english isn't my first language), and another one from the alliance of tobacco-free pleasure. They tested with a crown 4 kit, with realistic wattage and realistic drawlengths and breaks inbetween, and in different concentrations betweesn 0.5 and 7.5%
Both came to the same result that sucralose starts to break down at about 120C./248F., no matter at which concentration. Since it's a chlorinated sugar they found a few things like Chloroacetaldehyde, which i'm not sure if we should vape it..
Unfortunately so far there are no numbers about the amount of these chemicals and about how concerning this should be for us since we use it diluted to 10%-20%. I guess everyone has to decide for himself if he is fine with it or not.