OP has crafted the question thought fully:

S/he is not asking whether THERE IS any incentive but if THERE WILL BE  such incentive ever. Obviously other than what @gmaxwell has mentioned almost correctly, securing one's own assets there IS no direct financial incentive for running a bitcoin full-node in the current state of the technology either for bitcoin or for any other POW coin. But this fact doesn't prove anything about the potentials of POW cryptocurrencies in general.

That said, one needs to remain focused on the main agenda of bitcoin and its clone: building/developing a decentralized p2p electronic cash and recognize how critical it is to have the number of active full-nodes as high as possible to serve this sacred cause: decentralization.

So, I formulate the op's question as follows:
Is there any technical solution for a POW based coin to incentivize installing and maintaining active full-nodes preferably without disrupting the whole bitcoin technology?

As a matter of fact, investigating pooling pressure and mining centralization threats in bitcoin I've become convinced that an affirmative approach to the above question is inevitable part of a solid solution for the core problem of mining centralization.