I think, if anything.......this is the last wall Aqua/Goro have to cross for the revenge plan.....no matter what he choose to.
Putting aside Ruby/Sarina's excitement, what the writers said is 100% spon on. In-universe, this movie will ruin a lot of people's name and reputation, also the declaration of war toward dad. Just like a certain someone said......
The only ones who should kill, are those who are prepared to be killed.
If Aqua/Goro really does being serious toward his revenge, one kiss is all that remains toward the finish line...
unless those 2 writers also write a bed scene
But at the same time, Aqua's reluctance as a (former) adult and current biological brother of Ruby/Sarina is natural. I mean, just look at Ruby. Who knows what Sarina will do next if he gave her what she wanted
And like it or now, this could and would be the 'pot calling kettle black' point in future confrontation with the Kamiki.
Also while it was being talked about, Memcho is also right. A kiss scene between 2 rising stars gonna be the main point that sell the movies. Content of the movie is important, but they have to appeal to as many people as well to see the movie.
The kiss is the perfect bait.