That is one aspect of it, yes. You can now deploy multiple MODx sites from a single core (standalone sites with their own database and manager context) and/or use a single site to manage content from multiple virtual hosts (one database supporting multiple front-end contexts via a single manager). There will be better support for these scenarios in the installer when the beta releases hit the street, but I am testing various scenarios like this as I type this.
1) is it contexts that are going to enable me to manage several MODx websites and subdomains?
Yep; the code has all changed but all the same basic features are in place.
2) Will Revo 2 still have the same awesome SEF features that my clients love? I’m talking about keywords, custom meta chunks and the like.