Type class field

It would be great if we have the option to add the type class per field.

I have custom type class with more values than the foreignkey and every time I update the compoanent I need to make these changes

Example
foreignkey

<field name="xxx" type="foreignkey" class="inputbox"
label="xxxxx_LABEL_xxxxx"
description="xxxxx_DEC_xxxxx" input_type="list" table="#__com_xxx" key_field="id" value_field="xxx" required="true" multiple = "multiple"/>

Custom

<field name="xxx" type="customType" class="inputbox"
label="xxxxx_LABEL_xxxxx"
description="xxxxx_DEC_xxxxx" input_type="list" table="#__com_xxx" key_field="id" value_field="xxx" column="xxx" value_field_b="xxx" required="true" multiple = "multiple"/>

Thats why I need a filter options that depends on the cell value "b" from the column "column" thats why in my custom class I add a "where".

->from($this->table);
$query->where($db->quoteName($this->column) . ' = ' . $db->quote($this->value_field_b));

Or have the option in foreignkey to add the option to filter the drop values