Personally, I have seen quite the opposite effect of keyword stuffing. However, with RankBrain and other updates sometimes we go back through and re-hash and try things that previously worked, don't work, and might work. You should check out our article which is really a live case study to see if Google will index and rank it. Which can be found here.
Is keyword stuffing good for SEO?
As I stated from my experience I would typically say no, but recently I had a fellow marketer message me and showed me some examples and case studies of his own and it was all ranking. Not only was it ranking it was #1 for many high competition search terms. This leads me to believe maybe during one of the more recent updates as long as it isn't completely obvious and maybe even if it is that it still works as a strategy. That is why we created the post keyword stuffing does it work? So far it hasn't been indexed it's currently saying discovered but not currently indexed. We also are throwing some really spammy black hat links and tactics at it to see if we can get it to rank not only with its keyword-stuffed content but with links that other people say we should fear and don't work.
While we wait we can only educate ourselves off our past experience, which I have actually seen keyword stuffing hurt my SEO. However, I also can't disregard the fact that I have been shared sites that rank using this technique. This doesn't do much good when asking "Is Keyword Stuffing Good For SEO?" the main problem I have with the sites that were shared with me that are ranking #1 is it's very hard to isolate if the keyword stuffing has anything to do with the ranking, it may even be hindering them to show up for even more search terms. I say this because they have a really good link profile and even though the content is clearly focused on those keywords and jam-packed it still is very informational and has some real solid proof. So I guess with time we will have a more clear picture with the case study that I shared and many others that are going on behind the scenes.