Thank you for using Sublime Merge, and thanks for your feedback!
We currently have an equivalent feature to what you have mentioned.
When viewing the Blame view, the relative age of the line is indicated by the age icons, shown below:
Additionally, you can click on a line in the gutter to highlight all lines belonging to that particular commit, shown below:
You can also view the commit details of a given line by hovering over the line in the gutter, shown below:
Note that the commit hash is a link, and will navigate you to the blame view of that particular commit.
Let me know if you find this functionality useful!
Software Engineer, Sublime HQ