My suggestion is similar to the following (iced tea sweetened with stevia):
http://www.migipedia.ch/de/node/140969
I would like to see the Léger (raspberry) syrup sweetened with stevia. My children drink a lot of this syrup, a syrup sweetened with stevia would at least be more natural and probably healthier.
Even if the artificial sweeteners are probably neither carcinogenic nor harmful to the teeth, as they are sometimes said to be (see also the following article in Focus:
http://www.focus.de/gesundheit/ernaehrung/tid-13247/gesund-essen-die-wahrheit-ueber-suessstoff_aid_366088.html), stevia seems to me to be more natural and therefore better or at least on a par with artificial sweeteners. Decades of use, including on an industrial scale(http://de.wikipedia.org/wiki/Stevia_(S%C3%BC%C3%9Fstoff)) further support the use of this food additive, which has only recently been approved in the EU.
Of course, it remains to be seen how the taste changes will turn out, but I have no concerns about this.
Unfortunately, the selection of syrup varieties with no sugar is very limited.