Apparently we're already using it, see: https://github.com/xwiki-contrib/application-chartjs/blob/master/application-chartjs-ui/src/main/resources/XWiki/ChartJS/WebHome.xml#L1185
Hmm, my guess is that the JSX was loaded, but the JSX needs to load additional JavaScript code from some WebJars https://github.com/xwiki-contrib/application-chartjs/blob/master/application-chartjs-ui/src/main/resources/XWiki/ChartJS/WebHome.xml#L311 and those URLs don't have wysiwyg=true in the query string.