A quote from - Mark J. Kilgard • Principal System Software Engineer • nVidia
... the notion that an OpenGL application is "wrong" to ever use immediate mode is overzealous. The OpenGL 3.0 specification has even gone so far as to mark immediate mode in OpenGL for "deprecation" (whatever that means!); such extremism is counter-productive and foolish. The right way to encourage good API usage isn't to try to deprecate or ban API usage, but rather educate developers about the right API usage for particular situations.
The truth is that modern OpenGL implementations are highly tuned at processing immediate mode; there are many simple situations where immediate mode is more convenient and less overhead that configuring and using vertex arrays with buffer objects.
This fellow, MarK J. Kilgard has been publishing nVidia source code and documents on openGL since the 90's and has been doing so on behalf of one of the two biggest names in gaming hardware. With what that man said as a representative of nVidia, I feel that it is safe to assume that there will be no functionality dropped from OpenGL anytime in the near future so far as nVidia hardware and drivers are concerned. Now, I may be going out on a limb here by saying this but I suspect that AMD/ATI will be holding fast to this as well. My logic is as follows, despite the lack of public statement on this matter from ATI representatives, we can safely assume that AMD/ATI are not going to give nVidia the upper hand by all of a sudden taking out features that they currently support and have always supported.
One may also conclude from this that many other features of the OpenGL API that people are now afraid to use will not be going anywhere, nor should they.
Issues will arise for people that want to branch into mobile development if they are not careful with certain aspects the more "dated" API functions but it's also very likely that much of what is currently available in the broad OpenGL API will become increasingly available on handheld's, as their GPU's and driver models become more sophisticated. On desktops, OpenGL is almost fully backwards compatible going back 15 years. This is true for ATI, nVidia and even Intel has been following this model as best they can with their little purse-sized computers.