As mentioned in #700, it's sometimes useful to be able to use a list item as the basis for keyed updates, rather than a property of each list item.

That could be done a few different ways, e.g.:

{{#each things as thing @}}
{{#each things as thing @this}}
{{#each things as thing by thing}}

One potentially nice feature of the last option, apart from the fact that it doesn't have off-putting special characters, is that it could be more flexible — as well as by thing or by thing.id it could potentially be any expression:

{{#each things as thing by getId(thing)}}

Haven't looked into whether that's feasible. Just wondering about whether it would be desirable if so. Thoughts?