If I look on that page, it appears that RTF is using a similar-looking escape but in decimal rather than hex.
It would be important to define what is done with non-BMP characters? Will there be another escape for a six- or eight-hexdigit format for the codepoint, or will it be represented by two four-hexdigit escapes for consecutive UTF-16 surrogates?
the detection of decimal or hexadecimal codes can be a hard problem - string "12" is valid in both systems, but the numbers are different. So there should be external specification as an argument.