Nice article and I 100% agree on the importance of RPC (API) nodes but I must take issue with a number of facts and conclusions.

The cost or running a full API node (or RPC node) has dropped by orders of magnitude as the Hive code efficiency has increased, RAM requirements have been reduced dramatically and fast NVME storage has become dirt cheap.

I have posted here about how an API node can be built for around $750.

The issue is not cost but technical complexity and lack of idiot proof documentation.

It IS NOT the role nor duty of a Witness to run and maintain a RPC node.

While technically correct - it is not a mandatory requirement - it is something that is increasingly factoring in who people vote for witness and this is a good thing.

Changing the reward balance to have the blockchain pay people for running API nodes is fraught with complexity and controversy.
In my view it is just better to create a voter expectation that high ranking witnesses (or anyone hoping to become one) will run an API node.

As a backup witness I am receiving a producer reward or either around 1.3 HP every time I witness a block (it varies slightly above or below for reasons I don't understand). A top 20 witness receives 0.258 HP.