Player built stargates will probably be like nothing expected.
Very little to go off of, from that 2014 presentation.
More likely to be similar to other games (and some elements of EVE), that all players contribute x tokens/materials to an NPC entity, which then builds the stargate.
So though the stargate is technically “built” by players that contribute, its not owned by players.
Dunno where they will manifest.
Since they put so much stress on “all capsuleers” being able to get involved, its difficult to deduce.
That stargate then leads to a pocket system/constellation whatever, outside of k-space, with whatever mechanics. Probably some kind of system that attempts to encourage co-operation for PvE, with a dash of PvP alongside.
My guess would be a “battleground” type system, not dissimilar to Faction Warfare.
Something like the separate arena for world PvP in ESO, where you either fight over nodes, or PvE the peripheral content there.