Unfortunately it's not mini-PCIe. I am working on either the HLK-RM04 v2, which has 8MB flash/32MB RAM, or the HLK-7688A (or HLK-7628N, they are the same except for 75628N has two antennae), which has 32MB flash/128MB RAM.
It's unclear whether the HLK-7688/28 is compatible with new OpenWRT...