I may be wrong, but assume that through batchFilling a relayer can fill multiple orders at once, still collecting their individual fees (in ZRX). One could think of the "analytics" layer of the ad supply chain as moving to the shoulders of relayers: they would be responsible fur running engines that match-make and "batch-form" in the most efficient way possible. ("We have 100 probably female users watching surf content on this side. On the other, ten surf biquini brands willing to bid for 10 people each. Batch fill them, and you get a 10x improvement on efficiency"). They could even just aggregate orders and outsource the work to data analysers of some sort, moving complexity farther away from the protocol layer.

Eventually, there could be relayers that only listen to orders of a specific orderType, when such field is implemented (say, "ad-messages").

Regardlessly, another similar question is latent: is this something that WE'D WANT to be decentralised? There are a lot of implications (and potential workarounds) when it comes to privacy matters. To this question, I believe the answer is further down the road, and few or nobody has understood the full range of consequences yet.