I know he's the magical Slash Dragon to most of Merlin fandom, but to me he' more a conniving old dragon trying to work Merlin as much as he can to make events happen the way he wants them to by feeding Merlin ideas about his great future at Arthur's legendary side.

I admit I never gave the dragon all that much thought (then again I also have to admit I only started to really pay attention to the show around ep. 7-ish...), but this seems rather accurate after the last episode.

And what's tricky about the possible futures is that there always are so many consequences, so many variables. How would it have affected Arthur's trust in Merlin if Merlin hadn't shown up to save the boy Mordred? Or what if Uther had died in that fight against wraith!Tristan? Did either decision change things for the worse - or for the better?

unless he and Arthur are playing an elaborate game of don't ask/don't tell so Arthur doesn't feel he's betraying Uther - which I felt was a legitimate interpretation of the end of ep 10 with Arthur basically telling Merlin that he had been talking about Will and that he shouldn't keep dangerous info from Arthur again

That's more or less what I got from the end, too; they both feel it's simply something too dangerous to be really brought into the open...