There was a concern with version 1.2. Since then the guy at Coppermine has still continued to support tthe SSI.php. I don't believe it is too major a concern as the script is still up and available in their download section.
I seen 1 article on the SSI.php, about queries being to high as the primary issue. Most of the post about ssi I read are missing now.
Click here for SSI.php Posts at Coppermine