Er, let's be real for a second.
It was meant to be subtle so that people could construe it as a friendship. If you saw it completely differently, then the makers succeeded. However, the reality is that Korra blushed when Asami complimented her earlier in the season(when's the last time you saw a girl blush when a friend compliments her?) and that rather noticeably combines with the ending--which mirrored ATLA--of them framed the same way Varrick and Zhu Li were framed for their wedding.
The fact that that makers seemed to make it a point to eliminate any confusion about her having a relationship with Makko--"I will always follow you into battle", not a single ounce of romance, but that's the sort of comradery-esque statement one makes to a good friend or brother---right before that end scene suggests it through juxtaposition....The fact that right before that Makko was telling Prince Wu that he won't set him up with Korra also suggests that the question of romance was underlying those last couple minutes.
....Let's be real. It is essentially canon. Creators probably wanted to start their own Avatar-esque legacy by having the first non-completely-hetero Nickelodeon strong female main character.