I'll tell you now, if this fighting dragon had dragonite-esque stats and a semi useable movepool it would at the very worst be top of OU. If it has Salamence or Garchomp-esque stats (especially Garchomp) it'd almost certainly be pushed into uber zone unless GF introduces some changes of epic proportions to keep it in check or a terrible ability like defeatist (still... SR resistant).
Dual dragon typings with exploitable weaknesses/limitations are not only more balanced for OU, but also will do more for benefiting the metagame, as opposed to hindering it.
Some dragon dual types i'd like to see.
Dragon/Grass - limited by another x4 ice weakness and coverage, good defensive pivot type as well
Dragon/Fire - limited by rain and SR weakness
Dragon/Bug - limited by redundant coverage (most bulky psychics won't like meteors or outrages anyway, also has mediocre resistances/SR weak for defensive stat distributions)
Dragon/Rock - This could look really bad ass, limited by coverage unless it learns fire blast
I don't think a dragon/steel, dragon/water, dragon/fight would be healthy for the metagame assuming they get "suitable" stat distributions and movepools.
I'd like to see more of the Metagross and Tyranitar introductions, ie pseudo-legendary pokemon that aren't part dragon, that'd be great for the meta if we had less hyper powered dragons.
As far as existing dragons go, it'd be funny to see Salamence learn hurricane. Meteor + H pump + Hurricane would be incredible coverage in rain.