Ahh, good idea!

The only downside is that it would be more complicated to setup multiple targets.  For example, with overwrite, you can do this:

```ruby
date {
  match => [ "start" => "UNIX", "end" => "UNIX" ]
  overwrite => true
}
```

With the target approach, that would need to be split into two filters to achieve the same thing.  I suppose it depends on whether we want to continue encouraging multiple-patterns-per-filter (with "match" options and the like), or if we want to encourage single-function filters.  What do you prefer?