HEC is doing a training on HEC-RAS 5.1 at the SEDHYD conference in about a month. They will be discussing infiltration among other things. The link below is to the workshop for the conference.
I have heard multiple things for estimates of when it will be released and it is always changing, but probably within a year from now is a safe guess. Hopefully at the workshop, they can provide a more solid answer.
https://www.sedhyd.org/2019/openconf/modules/request.php?module=oc_program&action=page.php&id=112