Most of the conversation seems to have been about ensuring sufficient transaction fees are paid to miners. But what about the verifiers? Currently, all tx validation is done by volunteers. I think Satoshi initially intended for validators to double as miners, but in a world where the two are largely mutually distinct, how do we support the verifiers? And if we can't, isn't the network doomed anyway?
It is in users' self interest to validate. If you don't want to run your own full node, there are plenty of companies that will do the validation for you and charge you a fee. One reason to have a block-size limit is to make sure it always stays reasonable for a hobbyist, with a relatively modest expenditure or resources, to perform full validation at home. So I would say no, the network is not doomed in the absence of financial support for nodes.
Related to this is something I have not seen considered: an upper limit on hash speed per device.
No one has seriously considered it because the concept is a non-starter. Even if you could devise some way to enforce the rule on a per-device basis, there is no known and accepted way to stop a single entity from controlling multiple devices. People would figure out a way to control multiple hashing devices, and in such case your idea would introduce only added complexity and possible attack vectors and, I think, nothing positive.