I was looking at a flame graph of an ingestion workload with @dliappis, and it looks like we parse the JSON representation of the index request twice when a document has both a pipeline and a final pipeline.

It's hard to know how much we would save on this benchmark since not all data streams in this benchmark had both a pipeline and a final pipeline, but the cost of parsing index request into maps of maps via IngestService represented 4.06% of overall CPU time according to the flame graph, so this might not be negligible.
server/src/test/java/org/elasticsearch/ingest/IngestServiceTests.java
"version conflict, required version [%s] for pipeline [%s] but no pipeline was found",
                    version,
                    pipelineId
                )
            )
        );
    }
    public void testPutPipelineWithVersionedUpdateDoesNotMatchExistingPipeline() {
        var pipelineId = randomAlphaOfLength(5);
        final Integer version = randomInt();
        var pipelineString = "{\"version\": " + version + ", \"processors\": []}";
        var existingPipeline = new PipelineConfiguration(pipelineId, new BytesArray(pipelineString), XContentType.JSON);
        var clusterState = ClusterState.builder(new ClusterName("test"))
            .metadata(Metadata.builder().putCustom(IngestMetadata.TYPE, new IngestMetadata(Map.of(pipelineId, existingPipeline))).build())
            .build();
        final Integer requestedVersion = randomValueOtherThan(version, ESTestCase::randomInt);
        var request = new PutPipelineRequest(pipelineId, new BytesArray(pipelineString), XContentType.JSON, requestedVersion);
        IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> executeFailingPut(request, clusterState));
        assertThat(
            e.getMessage(),
            equalTo(
                String.format(
                    Locale.ROOT,
                    "version conflict, required version [%s] for pipeline [%s] but current version is [%s]",
                    requestedVersion,
                    pipelineId,
                    version
                )
            )
        );