From BenefitsLink’s helpful postings of Labor and Treasury regulatory agendas:
An agenda item shows Treasury’s estimate, perhaps optimistic, that the agency would publish a notice of a proposed rulemaking by December 2023.
https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202304&RIN=1545-BQ70
If you want to send suggestions even before a proposal is published or released, the agenda item names three lawyers assigned to the project.