Sure!
You can create a new field in site/fields/subpage/subpage.php
with the following content:
<?php
class SubpageField extends PageField {
public function input() {
$input = parent::input();
$input->data(array(
'field' => 'autocomplete',
'url' => purl($this->model, 'field/' . $this->name . '/subpage/autocomplete/' . $this->parent())
));
return $input;
}
public function routes() {
return array(
array(
'pattern' => 'autocomplete/(:all)',
'method' => 'post',
'action' => function($parent) {
$ids = page($parent)->children()->pluck('id');
return response::json(array('data' => $ids));
}
)
);
}
}
You can then use this in your blueprint:
page:
label: Page
type: subpage
parent: my/parent/page
Let me know if that works.
I have created a feature request issue on GitHub about integrating something like this into the core page field.