There is a Liir DN mission section named "Assault Carrier" that says it's for battlecruisers, and looks like it carries three. There's also a DN mission section for normal battleriders, so you need to pick the right one. I don't think it'll let you put battleriders in an assault carrier or battlecruisers in a battlerider carrier, though I haven't tested.
However, the battlecruisers seem to be treated as normal cruisers right now. Show up in reserves when built, drag-and-drop into fleets and take 6 CP, don't require carrier in fleet, don't show up in BR manager. Interesting that they can travel between systems without a carrier in fleet either, haha. They do work in combat, just again treated as a normal cruiser - can be placed in fleet manager, spawn separately (don't need to launch), fly and fight normally, etc...