I would hypothesize that Sherlock does love Molly romantically 

 (sherlock Meta by Queen_Nyeela)

I would hypothesize that Sherlock does love her. Romantically. I understand the argument that he meant the second I love you platonically. Incredibly fair argument.

I would counter that with the fact that it was already well established that Sherlock has grown to the point of loving people as friends and already loves and respects Molly as such. Sherlock is also aware that he can love his friends and we see him move beyond the immaturity of eschewing friendship in Series 3. Also, it was explicitly stated by Moffat during Series 3 regarding Molly and Sherlock's friendship: "Of course he loves her. He adores her." That ceased to be a question last series.

It seemed very intentionally set up that this particular game/test was about romantic love, not platonic, hence using Molly as leverage because she is already established to be in love with him. It appears that the question the scene was raising isn't about whether or not the underlying theme is platonic love. The set-up is expressly exploring romantic love. I would add John's assumption that the coffin might be for Irene Adler as more evidence that this scene was specifically questioning Sherlock's capacity for romantic love or his response to romantic love concerning himself.

Taking away the aforementioned question, it seems the question/debate is: Did Sherlock mean it the second time or was he just acting in order to save his friend's life? Any argument for the latter is incredibly valid and is as much right as the first given that it was purposefully ambiguous. Gatiss states this in an interview as well.

I argue for the former because of the development of those two characters, their relational development prior to this moment, explicit teasing, and the scene and aftermath itself. I would lean more towards the acting theory if his face had not revealed that he was coming to a conclusion. None of the parties present, Molly in particular, could see his face during the second declaration. He genuinely seemed to be realizing this for the first time and had nothing to gain from altering his facial expression because the primary person affected would not see it.

His response afterwards with the coffin strengthens my leaning. Do I think they were in an official romantic relationship at the end? Not even a little bit. I imagine Sherlock has no idea what to do with these feelings or even how to qualify them properly. I do believe they reconciled when Molly was told about the test. I think there is great potential and even likelihood for them to be together in an official romantic capacity down the line, though we may never see that on-screen.

I also think, ultimately, that it is all left to interpretation and a good argument can be made for many scenarios. It also seems very clear that Sherlock had sex with Irene Adler (probably more than once). However, I don't think his text at the end of Ep. 4 was to her because he says the same thing to Lestrade in Series 1 and Lestrade shows up in the montage afterwards. I do think it is fair and smart to say that he and Irene have had significant moments off-screen and that speaks to Sherlock's development and Adler's uniqueness/power as a friendly (very friendly) adversary of sorts to Sherlock. She is The Woman after all.

That's my long-winded theory, mainly because I have spent a good amount of time thinking about that scene given that, in my opinion, it was the most poignant of the final episode. I fall into the camp of people who really enjoyed it and Series 4 as a whole, though there were things I had pushback on.