[noggin]

Yes it will do 3D as 2D.

Is 3d iso already supported?

I don't believe so. I think MVC content currently needs to be re-wrapped as MKV (MakeMKV will do this) - though this is a fast process and won't lose you any quality (as it isn't transcoding).

If you compare th pi 2 with Intel celeron 847 with 2gb ram 1333mhz, how is performance? Better/faster?

AV performance is better as there is no 24p bug (the Celeron 847 won't do 23.976 or 59.94Hz output rates properly) and I suspect the Pi 2 also de-interlaces 1080i content as well if not slightly better.

The Celeron will bitstream HD Audio I think - whereas the Pi 2 will decode <192kHz 5.1/7.1 DTS-HD MA and Dolby True HD tracks losslessly to PCM (with 192kHz stuff limited to 4.0 or down sampled AIUI).

Can't comment on other speeds - but the Pi 2 is pretty snappy in UI terms as a result of its quad core CPU (and the extra RAM over the 512MB B+ makes a difference too I suspect).

I used to run a 1007U Celeron Revo and I wouldn't say the Pi 2 suffers in comparison (other than the lack of HD Audio bitstreaming meaning your amp lights don't come on!)

For other purposes a Celeron may be better if it has GigE - particularly for stuff like file serving, TV backends etc. The one limitation the Pi and Pi 2 share is that all the USB and Ethernet IO hangs off a single USB 2.0 bus. Intel platforms have more IO bandwidth usually. That said, this isn't a limitation I've hit when using a Pi 2 as a Kodi front-end.