I find it less and less likely that Bitcoin will be replaced given the amount of investment (both time and money) put into the system. If Bitcoin was remaining stagnant, I'd be pessimistic as well, but there are a multitude of improvements that will be deployed over the course of the next year.
I'll take all these improvements with a pinch of salt until they are actually in the wild.
Take the lighting network for example. The idea has been floating around for quite some time but in practice its still vaporware.
Yet, ask any bitcoin enthusiast what's being done to solve the scalability problem and the LN is trotted out as if it were already widely adopted. It's ridiculous.
Sidechains are an answer, for you, if you don't feel the current blockchains scale for your needs. For micropayments, or whatever. But they don't solve anything per-se because nothing is broken.
Pay to publish is a feature. It's the rate-limiting mechanism we'd need anyways, but directly tied into PoW and reward.
Make your coin and ask people if they want to use it instead of bitcoin. It's so easy, and you can be proven right.
