WildFly Preview should use a native jakarta variant of the Jakarta SOAP with Attachments API artifact.
This could be the Jakarta artifact or if we need changes that will never go upstream (which I believe is the case) then we need a org.jboss.spec.javax.xml.soap:jboss-saaj-api_2_0_spec.
One possibility is to consider adding a module to the existing 1.4 spec fork branch and using source transformation (see
JBMETA-422 as an example) to produce a native jakarta artifact. Probably a better option is to produce a new fork branch based on the Jakarta branch.