www.makemkv.com

1. Is it possible to backup or extract 3D video and to play it back from a sticker or hard disk to a 3D / HD TV?

2. Are there any special requirements?

3. Some blue-ray players state that they will play .MKV formats. Does this simplify matters for playback of ripped video?

4. Is there another format for blue-ray players necessary in order to reproduce ripped files?

The answer to all your questions depends upon your player.

Just because a player supports MKV and 3D does not mean it supports 3D in an MKV container. If you do a "backup", where you are copying the original m2ts files to the drive, a 3D-capable BD player should be able to play it in 3D. You are more likely to find a stand-alone media player (no built-in optical disk) that can play a 3D MKV file than a BD player, from what I have seen.

But every brand and model of BD player is different. The only real way to "know" is to find someone who owns the model you're looking at and ask them specific questions.