I'm gonna be a fucken old man with kids and grandkids at this point before the game's done.
What's the bottleneck in development here? What can we as consumers do to help speed this process up?
Dark Cookie has no plans to "finish" Summertime Saga. He has said so since at least 2017. As long as he has ideas, enjoys drawing characters and scenes, and fans want more content then he has said he'll keep going.
The code is the bottleneck. The posing of the thousands of images to the new display ratio is the bottleneck. Dark Cookie not being a good project manager is the bottleneck. Wanting to make Ren'Py do things most developers don't do with the engine is the bottleneck. There are others.
You are not a consumer. I am not a consumer. We are not consumers. We may consume the content, but we do not pay compensation in exchange for the game and therefore we do not meet the definition, legal or otherwise, of consumers. Dark Cookie makes the game free to everyone to download from his website and thus there are no consumers.
There are subscribers and the get other things for their membership. The game is not one of them.
They have already done what they can do to attempt to speed up the process. A number of them continue to bug him for content. However, he has also told people if they aren't happy with the progress, they should cancel their subscription. He has stated he gets bitched at by some people for doing what other people want and the when he does something else, he gets bitched at by another group of people. So he'll do what he wants, and what makes him happy, because he'll get bitched at no matter what.
And mass subscription cancelations won't do anything, because he's already got his bank to live off for many years. He'd just have to let go of the others and work on the progress on his own... Even slower than now.
Many would do similar if they were in his position and he is too much of a perfectionist to delegate the work to others.
Truth.