The project now involves dozens of companies, including BP, an oil major, and Socar and TPAO, the state oil companies of Azerbaijan and Turkey respectively.
Despite the years of planning and complexity of the project, its capacity, at 16bn cubic metres per year, is about half what European planners had hoped.
The SGC is set to meet just 2% of EU demand.
At market prices, SGC gas is competitive in Turkey and south-east European countries but not in the more distant western European markets.
Moreover, one of its developers is Lukoil, an oil firm backed by Russia.
In its current form the SGC therefore does little to curb dependence on Russia. That is unlikely to change, for two reasons.
First, in addition to NS2, Russia has devised its own plans to bring gas into southern Europe.
TurkStream, a pipeline to transport Russian gas across the Black Sea to Turkey, is scheduled to become operational this year.
Gazprom, Russia's energy giant (and NS2's sole shareholder), plans to build a second line to the EU and is negotiating its destination.
That would make the EU-backed SGC even less competitive.
Second, changes that would make the SGC more commercially viable are unlikely.
Advocates of the project argue that they plan to double the volume of exports if more gas becomes available, notably from Turkmenistan.
But the expansion would require new infrastructure and additional costs.
A way of avoiding that would be to feed new gas from Turkmenistan into SGC through a swap deal involving transit through Iran.
But renewed American sanctions on Iran preclude this option.
They also hinder the development of rich gas resources in Iran, which could have otherwise been exported to the EU.
At least one energy giant appears to take seriously the idea that the SGC could expand.
But it will not reassure the EU that this firm is none other than Gazprom, whose chief executive has said it would bid for access.
European rules require the SGC to open capacity expansion to the most cost-competitive supplier.
In that event, Gazprom's vast reserves and low costs would be hard to rival.
A project touted as a way to diversify Europe's gas supply might end up providing an additional route for its current, unloved, supplier.