I have no experience in that so please forgive me if it sounds a bit silly:
Is it possible to remove all "user layer" application and DalvikVM from an Android, just to obtain plain linux-based embedded OS with all libraries and drivers already configured? Does graphical environment requres DalvikVM? Could I get a classic terminal in that case?
Maybe somebody already have done something like this or knows good resources about it?
You can. Understand that it's running Bionic rather than glibc, and not everything you're used to having on desktop Linux will be available.
The simplest way to experience this is to shut the Android framework down with
adb shell stop (while running as root). At this point, anything you can do on the device is being done without the VM.
You can run native programs, sending stdin/stdout over ADB. You can interact with HardwareComposer to get access to the display, and use OpenGL ES to render stuff. (You might want to keep SurfaceFlinger around, but that's entirely native code.)
Having the VM available doesn't stop you from doing anything, so getting rid of it doesn't do anything but free up disk space.
You might be better off with a Raspberry Pi for hobby projects.
As far as I know, without Dalvik, you can't be running any application packages (APK's, like SystemUI or framework-res.apk) and JARs without which there would be no means to run the logical Android UI as we know.
Maybe you could get some shell running if you really know about Android and its stuffs.
And yeah, Android is not Android without Dalvik or ART :)
Removing them makes Android meaningless.
If you really are a Linux genius, you can completely wipe the phone's SD and somehow modify a Linux distro from its source and put it to the device, that too provided you know how to link the drivers (yeah, drivers are just compiled binaries, it'd be good if you had the source), and that's way more difficult than what one can think.. :)