I'm creating a dev environment, Server 2012 R2 + SP 2013, as a separate virtual machine. My main OS is Win 8.1 Pro. Now, I would like to dual boot to this dev environment. I already know how to achieve that, but the problem lies with AD controller, which needs to be a separate machine. How can I run system from vhd, and simultanously have AD VM running? Can I run another virtual machine inside this SP DEV machine?
Short answer is that your scenario is not possible.
However, your need to dual boot probably arose from a need to maximize the use of your hardware.
I have found that is it possible to create a full SharePoint farm on Hyper-V, if you use "headless" (GUI-less) installs for the AD controller and database servers, as it consumes far less memory.
I have written an article for how I did it here: http://www.shailensukul.com/2013/09/installing-full-sharepoint-2013-load.html
As you have Win8.1 pro you can use Hyper-V.
By using this you can create your environment. You need licences for each VM though so depending on your circumstances this can be expensive. An MSDN subscription usually helps or you can use trial versions of Windows, SQL and SharePoint.
If you configure remote desktop you can easily logon to the machines from the host PC.
Try running your VM with Hyper-V or create it with VMWare.
UPDATE : You can create a virtual switch on Hyper-V to create a bridge between the two machines.