During the discussions that led into the current radial-gradient() syntax, there was an extended proposal that included the ability to specify the geometric center and color focus of the gradient separately. That proposal is summarized in
https://lists.w3.org/Archives/Public/www-style/2011Nov/0210.html
and consists of a from <position> or from offset <offset> argument (depending on whether an absolute position or relative offset is desired), and was slated for consideration for a future level of CSS Images, so copying here.