Include background to ideas for future work in related work chapter of master thesis? First of all I hope this question is not too trivial for this site. It does say in the FAQ:
"This site is for academics of all levels". Furthermore, this question should be helpful for other novice researchers who want to write a paper or thesis.

I have worked for a good while with my MSc. thesis and what I did initially was to read a lot of related work in the research area of my project and also in perhaps more peripheral areas that initially seemed very interesting. 

This initial review is the basis for a related work chapter that I have written. I was fully expecting to prune a lot of this text and have also done this according to what I eventually ended up doing. However, a lot of the descriptions of research that I have in the current version represent very interesting ideas for extensions to the current approach that I want to write about in a future work section.

Should I keep the sections in related work that are about research areas that I have not ventured into, that are not directly comparable but do represent possible extensions?

If possible I would also like someone to explain how related the related work section/chapter should be.
While is always interesting to venture in new areas while writing your thesis, the overall advise I usually get is to keep a solid straight line story, this way the readers won't feel confused on why did you put certain stuff that you did not use at all.

The main objective of the related work, should be to put your own work into context with respect to your peers, but your present work, not your future work. You would be basically citing your future work, which would not be good.

You can always write a Future work section that can be as long as you want.

My overall advise when writing your thesis (especially for Masters) is to keep it simple and straight.