Michelle, totally agree that Kelly seemed inspired by the news, not upset, as it gave her hope that two people found their way back to each other like that meant it would happen for her and Brandon again. At least that's how I always saw it.
I don't think either of them should be referred to as '2nd best' b/c she chose herself in the 1st place b/c she loved them both. She chose Brandon eventually of course though, proving once and for all she ultimately will always have such a strong love for him.
And yes, when she's in hospital, she tells him she still loves him, and that she had everything (when she was with him), and lost it all (when she lost him). That confirms my faith in this couple as being an ultimate one of the show.
Dylan's S7 absence made no difference. BK weren't default b/c all their build-up was clear foreshadowing of the fact that they were meant to be together. Kelly had feelings for Brandon way back in the 1st season. She'd always wanted to be with him.