Very good and sharp analysis of current PLAN capabilities on the ground,
@jhungary . You are right that these islands are some 600, 700 nautical miles away from the nearest home port of Hainan Island. This can be a vital strategic issue in the case of strategic resupply, or force projection abilitie(s). I think that as we speak the current underperformance of such islands such as Fiery Cross Island and other key holdings in the Nansha Island(s) is due to the lack of naval and air military presence in those islands. However, from my analysis of such islands, i can't help but notice these:
Newly genesized islands such as these, are capable to be armed with at least a regiment or battalion sized force, and can easily hold up to two to three squadrons of fighters (even more). They can easily provide air defense batteries of S-400 or the HQ-9, armed with impressive radar systems such as the HT-233, YLC-2. Arming these islands with 4-5 batteries of S-400 or HQ-9s would make these practically impregnable from air to ground attacks, and would greatly inhibit foreign air force projection / interdiction or inhibit carrier air wing enforcement.
Secondly , looking at the dredging activity in the central and perimeter of the island, i can see that they will probably construct a deep sea port in this island, which can eventually host and dock larger naval systems, particularly more heavy destroyer classes of the PLAN South Sea Fleet, specifically the Type 52 B,C,D. In particular the Jiangkai Class Destroyer, which has already been deployed en masse to the Nansha Islands.
My prediction is that , utlimately, after islands such as these are fully operational and with naval deep sea ports created and ready for access, they ultimately will be forward deployed bases for their destroyer squadrons or even be host to rotational processes of their current Liaoning Carrier Battle Group. Let us remember that they are currently constructing 2 more carriers of the Varyag / Liaoning Class, i assume those two will ultimately be stationed for the North Sea Fleet and East Sea Fleet, respectively. Basically a carrier per fleet.