Real cash usage is gradually declining, but approximately zero of that difference has been taken up by Bitcoin: https://www.frbsf.org/cash/publications/fed-notes/2018/novem...
Merchant adoption is not just stagnating, it's in reverse: https://www.bloomberg.com/news/articles/2017-07-12/bitcoin-a...
If you contrast this with the speedy rise of M-Pesa, it's obviously a failure as digital cash. It's also a failure as compared with things like Venmo, which are all popular with people doing cash-like things: https://money.com/venmo-cash-app-zelle-better/
So if it's not good for the stated purpose, what's it now good for? No speculation about the future please. Just name a specific, significant group of users, state their problem, explain how Bitcoin solves it better than alternatives (better on their terms, not yours), and link to statistics showing sustained, rising adoption.
The best resource is financial twitter (fintwit). The news breaks there, the discussion happens there, and loads of meme-ing also takes place (which is always a nice to-have in a serious place). The only drawback is that most of them lean exactly the way I do. So I can bear the place, but I miss out on a bunch of opposing opinions and it's always a challenge finding someone on the opposite side of the fence.
