Rather than simply view the SCO as some form of new Warsaw Pact to rival NATO, it shoudl be viewied as an emerging proto EU with a more robust security aspect. Its growth is very much of the "organic" variety (to use the cringeworthy cliche) and concentrating into areas of very genuine concern and interest to its members, trather than trying to formulate Ideological polices that will maintain little interest or adherence from the members.
This week (Friday) the SCO is holding a conference on Afghanistan in Moscow, which through its far more rounded ability to deliver security and assistance on all levels through a single organisation and attract the support of all the Regional Players, is expected to upstage the NATO gathering shortly afterwards.
It will be interesting to see what happens in 10 to 20 years time when the SCO has become a more matured organisation and the nations within it will have enjoyed up to two decades more of growth. I have no doubt it will have expanded, certiably to have included the rest of Central Asia and the many of the CSTO countries.
The interesting test will be to see if at that time, the SCO will be able to present Development and Security models, attractive and more relevent enough to tempt recent Accession nations out of the EU and into it instead?
The SCO is really a rival to the EU and should be viewed primarily in that light.