Line number is simple, but as has been discussed in these issues before, column position has multiple possible definitions in a UTF-8 document:
. byte number . code point number (most code points are more than one byte) . character number (some characters are more than one code point) . glyph number (some glyphs are more than one code point) . visual column number (some glyphs are zero, narrow, single and double width, and then there is non-monospaced fonts)
The environment variable name therefore should be explicit what it provides. Byte number is the only one easily available.
As the command run from a snippet can only see files stored on the filesystem, they can't see anything in the buffer, so as @philiprbrenan pointed out line/column values may not match the buffer if it has been edited and not saved.
So the usefulness of adding these values would seem limited.