It depends on the type of link aggregation - many types will limit a single stream to a single interface (and therefore 1Gb), but others can bond multiple ports together under the same logical link.
It does require support at both ends of the link but some implementations can work more like a single, wider link. It's sort of the same principle as how multiple DOCSIS channels are bonded to give a final, faster connection visible to higher layers.
I've not seen this explicitly stated but I wonder if this is what the DOCSIS 3.1 modems supporting link bonding are doing:
https://motorolamentor.zendesk.com/h...an-one-device-
I've no idea if the Hub 4 supports that or if it could be added with firmware updates.