You are not dreaming - this is already possible using RockMigrations:
<?php
$rm->migrate([
'fields' => [
'myfield1' => [
'type' => 'text',
'label' => 'My field one',
],
'myfield2' => [
'type' => 'text',
'label' => 'My field two',
],
],
'templates' => [
'mytemplate' => [
'fields' => [
'myfield1',
'myfield2',
],
],
],
]);
If you don't like PHP arrays for whatever reason simply use json_decode( _your_fields_and_templates_as_json_string_ ) instead...
I'll release a new version soon that makes it a lot easier to get started with RockMigrations though the API will 99% be the same as in the old module.