I believe the pavement concessions out there are an issue. The 737-800 doesn't have a low pressure tyre option, which is why the A320 is a better option(and why VA uses the A320 to Cocos Island). Not sure about the 170 but 190 can be EDTO rated, tho like all things mega $$ and not an easy option for operators(route proving etc). VA and nearly all major operators are getting rid of them for a reason, nearly 737 costs with far less seats.
WX can be terrible out there but the huge amount of diversions has mostly been fixed by the RNP approach out there which gets you down to 360 feet in 2km vis one end and 314 feet and 1.7km at the other end. Issue is as far as I know that JQ/QF/NZ/VA are the only RNP-AR approved operators in this region, anyone else is doing RNAVs with 630 feet and 3.5km vis minimas, which when it's crap in NLK doesn't even get you close.
All of the Islands (Christmas/Cocos/Lord Howe/Norfolk) are not viable commercial ports without the government subsidies. NZ has never paid a subsidy for the AKL-NLK and AU isn't going to.
Next interesting point is what happens to Lord Howe when QFlink doesn't apply to renew Lord Howe, the Q200s are getting long in the tooth and costly to keep them just for there, what aircraft and operator has the capabilities to offer the service the island has had for years with the Link?