The picture above was taken by Alexei Watson who states that the new stock recovery in Android L has a few new features. You can now Reboot to Bootloader, and Power down.

If you want to unlock your phone’s bootloader, then you’re in great luck–we have a step-by-step guide on how to unlock the Galaxy Nexus’ bootloader.

The unlock button will reboot your device, unlock the bootloader, wipe all your data, and then return you to the Android 4.1 setup screen.

Simple guide to boot OnePlus 2 into fastboot or recovery mode and perform a factory reset.

9. Wait for your boot screen to appear on your phone. Once it does (it’s a big Android with START), type: fastboot oem unlock (Again, it’s ./fastboot oem unlock on a Mac) 10. A bootloader ...

First off, the bootloader isn't part of Android, it's what lets the device boot into Android. Device manufacturers generally want you to stick to the version of Android they preloaded on the device.

Unlock your bootloader, but do not flash your custom recovery yet. Reboot. Your device will force-boot into stock recovery, wipe data and cache, then reboot again.

In other words, we can't use ADB to jump directly to Sideload mode today, but if we are willing to flash a new custom recovery, we'll probably be able to do this in the next few weeks, regardless ...