> Big tech is moving from an exponential phase to a sigmoidal one.

I'd propose a modification of "Big Tech" to "Ad Tech" or "Marketing Tech".

There's still exponential growth available in nascent or underdeployed technologies -- AR/VR, blockchain/crypto applications (beyond just ICO), AI, IoT, Autonomous machines (maybe that's AI to you), are a few that come to mind. I'd wager the next "Google" will be in one of those, OpenAI may already be it.