I would like to provide developers the most up to date information as to
whether a file they are making changes to is also being changed by
someone else.

Some kind of 'in-eclipse' notification when a user edits a file which
another user:
a) has saved locally and hasn't yet checked-in
this would be ideal, but possibly more difficult that the options below.
b) has checked-in to a repository workspace
either to a repository workspace that flows to the same stream or any stream
c) has delivered to the same stream (or any stream!)

It would be nice if the user got some sign when first editing a file,
that someone else was making / had made a change that overlaps with
their own when they started to make a change to the file. Adding an
adornment to the file in the Package Explorer view would also be a help.

The reason for doing this is to assist earlier understanding as to the
extent of changes to a file that is common to two tasks being worked to
minimize subsequent churn in accepting / merging in changesets.

Any thoughts on how to achieve some of this (or equivalent) using the
released RTC, much appreciated.

Thanks,
Jeremy