Summary of the new feature/enhancement

If we permit the IsFilter property on a scriptblock to be either internally or publicly settable, we can make more effective use of anonymous scriptblocks as impromptu filters. These could be utilised in a pipeline context to emulate ForEach-Object without a lot of the extra features and overhead afforded that cmdlet, for scenarios where speed is significantly more important.

Proposed technical implementation details (optional)

This property needs to have at least internal set so that the following property that references it can also be set here instead of just throwing:

With that permitted, we can perhaps implement an operator or an attribute such that this becomes possible as an impromptu ForEach-Object with none of the fluff.

1..10 | & [filter]{ $_ % 3 } 

Currently, this is possible by specifying the process block, but this syntax becomes quite cluttered very easily:

1..10 | & { process { $_ % 3 } }