If you have fabric determinism like Infiniband, and capacity reservation on the receiving side, you can just dispose of connection paradigm, flow control, and thus get great deal of performance, while simplifying everything at the same time.
I do not see much use of it though unless you are building something like an airplane.
The uncounted PhD hours spent on getting networks to work well do amount to something.
Dealing with RDMA aware networking is far beyond the ability of typical web developers.
Deterministic Ethernet switches cost a fortune, and are lagging behind the broader Ethernet standard by many years.
Making a working capacity reservation setup takes years to perfect as well.
99.9999...% of web software will most likely *lose* performance if blindly ported to RDMA enabled database, message queue server, or caching.
If you don't know how the upoll, or iouring like mechanisms work, you can not get any benefit out of RDMA whatsoever
I once worked for a subcontractor for Alibaba's first RDMA enabled datacentre.