Something Else GRRM Could Be Struggling With (Spoilers Extended)

In the past GRRM has mentioned how dark of a book The Winds of Winter is going to be:

With quotes like:

Question about "The Forsaken"

GRRM: “Yeah, that is a dark chapter. But there are a lot of dark chapters right now in the book that I’m writing. It is called The Winds of Winter, and I’ve been telling you for 20 years that winter was coming. Winter is the time when things die, and cold and ice and darkness fills the world, so this is not gonna be the happy feel-good that people may be hoping for. Some of the characters [are] in very dark places…In any story, the classic structure is, ‘Things get worse before they get better,’ so things are getting worse for a lot of people.” -SSM, Spanish Interview: Guadalajara, 2016

and:

The number of POVs will be declining throughout TWOW. GRRM does not intend to add any more POVs. In fact, the number of POVs is about to decline. “Take your bets,” GRRM warned. -SSM, Tower of the Hand: 3 September 2012

The reader should expect a lot of dark, and bad things (including death) to a good amount of our favorite characters. As the writer of Ned's execution, the Red Wedding, etc., I don't think that it is that he finds it hard to do (he did write the Red Wedding chapters of ASOS last), just that he could be struggling with giving the reader just enough "light" to not actually just be depressed with what is going on the whole time.

Obviously there are probably other issues as well that go into him slaying the Son of Kong (size, combining plotlines, etc.) that probably have caused more of an issue, but I can't help but wonder if he's thinking in the back of his mind, "They've waited 10 years, they deserve just a little bit of happiness".

TLDR: The darkness in TWOW may be a little hard for GRRM to give to fans after making them wait so long even if the primary factors for the delay are elsewhere.