c) Provide the changes, including source code, with every copy of the
modified Vim you distribute. This may be done in the form of a
context diff. You can chose what license to use for new code you
add, so long as it does not restrict others from changing the
official version of Vim.
This prevents someboy from adding a patented item and not permitting
others to add a similar item to Vim.
I am not convinced those words really do this job. The difficulty is
that, in such a case, it is not "the license for the new code" which
restricts others, but rather the patent which does so.
Maybe these words would do the job:
c) Provide the changes, including source code, with every
copy of the modified Vim you distribute. This may be
done in the form of a context diff. You can chose what
license to use for new code you add, so long as it
permits others to include all or any part of this new
code in a subsequent official version of Vim.
And you might want to add
"... and release it under this License."
