Right now we can create custom configuration based on presets, however I think it would be worth allowing custom presets also.
This would mean opening up the Preset interface so for example a framework could maintain their own Preset file and users can then use the preset, just by pointing

I don't think it is correct to generate code which will put an argument with a default value before an argument without a default value.

In the example the generated code produces a function like that:

function bar(int $a = null, string $b, bool $c, callable $d = null) : float

This means the first argument is optional, but the second and third aren't.

I realise = null i