> I think the solution is that advertisers will just need to give up the idea of having reliable metrics on ads, since that's the source of the problem.
One of the things I found incredibly annoying when I was working in this area was the fact that definitions of some metrics can be so drastically different, eg. viewable impressions, completed view impressions (in video) - these difference were so huge that a video played off screen, a video played with only 1px (or 50% height) visible - have been treated as exactly the same thing.
I heard about a company that changed their way of measuring these metrics to something more realistic than... well, a video playing off-screen, whilst increasing prices, which sounds like a decent move - they ended up losing ca. 70% of their revenue.
The problem is that it's really difficult to explain your customers that you've been potentially lying to them (or at least that's the impression they might get).
Regarding the performance footprint - I recommend taking a look at the VAST/VPAID spec. It's not uncommon for an ad to fetch 3-4 xml files containing dozens of tracking pixels coming from 10s of domains. There's also no guarantee that any if the intermediate VAST files contains the right content, how long the chain is or where it comes from.
[EDIT] disclaimer: I might've used incorrect names here, since it's been quite a long time since I've worked in this area, I hope you still get the idea.