The MariaDB vs PostgreSQL debate continues to rage in my firm :-( and its fuelled by this somewhat famous uber blog post. I found some interesting discussions about write amplification mitigations here. My question is, did anything like this get release as part of PostgreSQL 10 or 11? I would search the documentation, but I'm not sure what it would be called.
No, nothing major along these lines has been released.
Main answer: Per this presentation, Postgres 10's introduction of a logical-replication option (as opposed to the byte-replication we had natively * before) reduces write-amplification on replicas to a degree, though – as of my most recent edit to this post – the fundamental complaint of Postgres tying indexes directly to CTIDs (which requires all indexes associated with a row to be updated when that row has a change, an op that must also flow to replicas) still stands.
* Logical replication has been available as a simple plugin since 9.4, and in some form or other since long before then.
Aside: Apparently, write-amplification was not the only reason for Uber's switch according to this thread (apparently backed up by some messages which appeared on the mailing list); difficulties with performance were only part of the reason they decided to switch.
A presentation discussing the legitimacy of Uber's complaints against Postgres can be found here. It contends that some of the problems Uber's post highlighted either had solutions or were self-caused.