Every platform will be replaced at one point, even facebook at some point in future. The question is when and with what kind of platform/why there is need to. Instagram will also be replaced at one point in future, that’s a normal process.
You are right about this.
Even if soma had great success and become mainstream it will be replaced either.
They will only be replaced if something is 10x better. Anything that is 2x better wont conquer the market. Its a general rule in buseniss:
http://www.businessinsider.com/your-product-needs-to-be-10x-better-than-the-competition-to-win-heres-why-2011-3?international=true&r=US&IR=T
Hard to understand how you can gauge that a platform is ten times better than another.