It's no way that Bitcoin will become a boring investment, the fluctuations of the price gives a lot of opportunities for people to make profit, but I see the enthusiasm of Bitcoin is slowing down, I think this is the cause of alt coins, but Bitcoin still one of the most traded crypto
The OP think it will just stay the way they are if that scenario happened.
I don't think that it will happen. The probable reason is that Bitcoin at that time will be having a good price. At that time, Bitcoin will not be stagnant, a lot of people will be using it and hoping they can invest and get on with the profits other people are having. Altcoins will have their movements too and I think that is more exciting than ever.