Lambda is similar, we have 'Serverless' and I'm hacking on Apex (https://github.com/apex/apex) just to make it usable. I get that they want to create building blocks, but at the end of the day consumers just want something that works, you can still have building blocks AND provide real workable solutions.
I was part of the team migrating Segment's infra to ECS, and for us at least it went pretty well, some issues with agents disconnecting etc I sort of wrote off since ECS was so new at the time.
Another annoying thing not mentioned in the article is that the default AMI used for ECS is not at all production ready, you really have to bake your own images if you want something usable. I suppose this is maybe because there's subjectively no "good" defaults, I'm not sure, but it's a bit of a pain.
ELB for service discovery is fine if you can afford it, I had no issues with that, ELB + DNS keeps things very simple. I'm not a huge fan of all these complex discovery mechanisms, in most cases I think they're completely unnecessary unless you're just looking to complicate your infrastructure.
I also think in many cases not propagating global config (env) changes, is a good thing, depending on your taste. Scoping to the container gives you nice isolation and and more flexibility if you need to redirect a few to a new database for example. You don't have to ask your-self "shit, which containers use this?", it's much like using flags in the CLI, if we _all_ used environment variables in place of every flag it would be a complete mess.
EDIT: I forgot to mention that the ELB zero-downtime stuff was awesome, if you try and re-invent that with haproxy etc, then... that's unfortunate haha. No one should have to implement such a critical thing.