I also like the Str + Con
option a lot. (for purely selfish reasons, I admit. as this change would allow me to use a str 18+2 at first level while maintaining all the feats I need)
Although str + dex or str + wis would also fit a lot of classes too. Str + Dex I could also see that happening and opening up Rogues and ranged rangers (not iconic, I know, but oh well). A lot of wis based classes would fit too thematically if that's the option. I also agree Cha covers the Sorcerer / arcane side of dragons, so in this edition are not likely to be Wizards. If anything, Str or Con, AND Cha OR Int, would make them great at a large number of classes. I hope they fix the attack progression of breath attacks too. Melee clases can't spare the feats to boost it, especially since without implements via making the breath an arcane power, it can barely hit. Hopefully there will be some way to use regular magic weapons as the implement type for boosting DB.
Probably won't happen due to balancing with other classes needing implement proficiencies, but one can dream, can't they? It seems bad that racial powers can't benefit from implements by default. Let's hope this oversight can be corrected. The only balance issue is for those who can re-spawn their DB, AFAIK. And those are already the dragon magic sorcerers, who probably have DB - boosting implements anyway.