There also seems to be something of a standard already. From
https://www.dokuwiki.org/devel:plugin_survey:compatibility#syntax
"Although there are no rules for syntax mentioned some “de facto” standard has evolved. In this survey it looks like a majority of special patterns are either {{…}} (160 cases) or ~~…~~ (80 cases). A very common entry/exit pattern (231 plugins) is something like an XML tag even if some use upper case letters."