Don't disk-based data structures have similar constraints? There too there is no ability to ship computations and we try to optimize for minimal data round trips.
RDMA instructions are (1) more expressive than disk operations, from what I understand (support compare-and-swap, fetch-and-add, etc.) and (2) have different latencies and bandwidths (on the order of 1us latency, 20 GB/s BW).
This paper is mostly about proposing new RDMA instructions, such as a relative load/store, that could make remote data structures more efficient.
NVMe defines compare and atomic compare-and-write operations, but I'm not sure if there are any notable users of them. They certainly aren't exposed by typical file IO abstractions. There's nothing like a fetch-and-add in any typical storage protocol that I know of.
In the context of this paper, though, "far memory" is referring to memory outside the local system that is accessed using RDMA instructions.