Camelot
Adventurer
Str/Con could be a good option as Dragonborn has two racial ability tied to Con.
But I guess for that very reason WotC may hesitate to make Dragonborn into a high Con race. High Con dragonborn maybe too efficient.
Also, there are so many Str/Con races (Dwarf, Goliath & Warforged).
Considering the lack of Str/Int race (only Genasi), I vote for this combination.
It was also thought that Str/Con would be too efficient for a dwarf too.
If there is one thing we have learned, it's that Wizards doesn't care about making races (and other things) just to fit a niche. The fact that there are more Str/Con races than Str/Int races won't affect their final decision. Which will probably be Con, because it's both thematic and efficient.