Magento2 Layout XML – How to Remove Block

I couldn't find a way to do this with layout either but here is an example of a way you can do it with observers (providing they extend the Template block)...

Create your events.xml in etc/events.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="view_block_abstract_to_html_before">
        <observer name="remove_block" instance="[Vendor]\[ModuleName]\Model\Observer\RemoveBlock" />
    </event>
</config>

Create the observer

<?php

namespace [Vendor]\[ModuleName]\Model\Observer;

use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;

class RemoveBlock implements ObserverInterface
{
    protected $_scopeConfig;

    public function __construct(
        \Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig
    ) {
        $this->_scopeConfig = $scopeConfig;
    }

    public function execute(Observer $observer)
    {
        /** @var \Magento\Framework\View\Element\Template $block */
        $block = $observer->getBlock();
        if ($block->getType() == 'Magento\Backend\Block\Dashboard') {
            $remove = $this->_scopeConfig->getValue(
                'dashboard/settings/remove',
                \Magento\Store\Model\ScopeInterface::SCOPE_STORE
            );

            if ($remove) {
                $block->setTemplate(false);
            }
        }
    }
}

Basically the _toHtml checks to see if there is a template. If there isn't it returns ''.

EDIT

After some more digging i have found a way to do this further up the chain.

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="layout_generate_blocks_after">
        <observer name="remove_block" instance="[Vendor]\[ModuleName]\Model\Observer\RemoveBlock" />
    </event>
</config>

And the observer...

<?php

namespace [Vendor]\[ModuleName]\Model\Observer;

use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;

class RemoveBlock implements ObserverInterface
{
    protected $_scopeConfig;

    public function __construct(
        \Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig
    ) {
        $this->_scopeConfig = $scopeConfig;
    }

    public function execute(Observer $observer)
    {
        /** @var \Magento\Framework\View\Layout $layout */
        $layout = $observer->getLayout();
        $block = $layout->getBlock('dashboard');
        if ($block) {
            $remove = $this->_scopeConfig->getValue(
                'dashboard/settings/remove',
                \Magento\Store\Model\ScopeInterface::SCOPE_STORE
            );

            if ($remove) {
                $layout->unsetElement('dashboard');
            }
        }
    }
}

As near I can tell, you can do do this at the PHP level, but not (as of the 2.0/GA release) at an XML level.

The layout structure object (Magento\Framework\View\Layout\Data\Structure), which is the single class that controls which elements are in, or not in, a specific request's layout, has an unsetChild and unsetElement method.

However, there doesn't appear to be any layout XML directives that allow you to pass through a raw unsetChild or unsetElement command.