It was a basic assumption of satoshi that mining will remain decentralized since he assumed that 1 miner will be 1 node, and everyone will mine on his PC with the CPU.
This is incorrect. Satoshi had this to say on the subject.
The current system where every user is a network node is not the intended configuration for large scale. That would be like every Usenet user runs their own NNTP server. The design supports letting users just be users. The more burden it is to run a node, the fewer nodes there will be. Those few nodes will be big server farms. The rest will be client nodes that only do transactions and don't generate.
(Sauce)The scenarios are playing out as expected with an end game of a cartel of miners, users with web wallets and the occasional hipster running their own full node.
The idea of economic incentives for full nodes is an attempt for already committed early adopters, to squeeze a few crumbs from the miners' table in the face of the inevitable. In the end, most full nodes will be run by the miners so it is a zero-sum game.