Will there ever be any monetary incentives to run a full node?

[zeuner]

If a SPV wallet doesn't implement checkpoints, it would theoretically be fairly easy to trick the SPV wallet by building an alternative chain. Since that chain is the only chain the client will see, it is assumed to be the longest valid chain. With a checkpoint system, the attacker will have to build the chain after the checkpoint which is significantly more difficult but will not require anywhere near 50% of the network's hashpower.

You see, the reason why 51% attack works is because it can generate valid blocks faster than the rest of the network. You don't need anywhere near 51% of the hashpower if you have all the time in the world. I can probably generate a block with enough POW in a few days if I purchase enough hashpower. I don't need to worry about someone else generating the block before me because the client won't be able to see it.

51% attack is about receiving coins on a wrong chain, not sending. So even if you will be able to isolate SPV wallet owner on a wrong chain how it will help to attack him?

It could trick them into believing they received coins via an invalid transaction.

Well, this is something very unlikely to happen. If we talk about regular user, transaction can be very easily checked on any block explorer which is hard to fake. Big players usually use more subtle tech than just SPV wallet/node.

And how exactly would the block explorer work without a full node providing the data?

[Joe_Bauers]

OP has crafted the question thoughtfully:

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, recognizing 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 in the framework of any solid solution to the core problem of mining centralization.

I actually started working on this a few years ago for a new alt-coin (yes yes, I know) called Poncoin <- Proof of Node. Even came up with a mascot Ponnie the Pinecone lol. Essentially each wallet would have a static (or dynamic) "PON address" that would be hashed with the ip + block to provide key: (ip address + pon address + relayed block = key) That hash would then be added to each relayed block. A certain amount of blocks later, let's say 120, as long as full node was still active, they could redeem a set value. To somewhat alleviate the issue of bad-actors running multiple nodes, a lottery would also be implemented to distribute reward.

There is ABSOLUTELY no reason there shouldn't be a reward for running a full node to answer the initial question, (just ask your local ISP if they think their bandwidth should be free) but I am not as smart as a hair on gmaxwell 's head, so I'm sure there are lots of flaws in my idea. Which is one of the many reasons Poncoin was never done. 

[pooya87]

Essentially each wallet would have a static (or dynamic) "PON address" that would be hashed with the ip + block to provide key: (ip address + pon address + relayed block = key) That hash would then be added to each relayed block. A certain amount of blocks later, let's say 120, as long as full node was still active, they could redeem a set value.

It depends on what you mean by "check if still active", I can write less than 100 lines of code and using about 50 MB of memory and virtually no CPU usage and 0 storage, I can run a fake node that is capable of appearing "active" by accepting incoming connections, relaying the block(s) I want to receive the incentive for.
All it takes is an open socket, keeping a couple of hundreds of headers (<50 kB) and a handful of blocks (<40MB) in memory, not relaying transactions, not verifying anything, not storing anything on disk either.

[Wind_FURY]

If have one question. Who should pay for the monetary incentive for to make users run their own full nodes? The miners? Mining pools? Developers? Exchanges? I believe monetary incentives can be used for political agendas.