The SCO's long-term plan is to increase Islamabad's strategic autonomy so it may become immune to relentless Washington pressure/humiliation/violation of sovereignty. And getting Pakistan into the SCO is a sterling mechanism for both Moscow and Beijing to "force" Islamabad to fine-tune its stance towards Afghanistan.
Both Moscow and Beijing also want Afghanistan - like Pakistan - to become a crossroads of rail, roads and pipelines from across the Indian Ocean and Eurasia. That explains Beijing using the privileged Sino-Pak axis to "seduce" Kabul and, within the SCO, investing in "all-weather" strategic partnerships all across the board.
Moscow has also found the SCO immensely helpful. What Washington really wanted all along in Central Asia was for virtually unlimited gas from Turkmenistan to flow to Western Europe - via the also eternally plagued Nabucco pipeline - and thus cut off Gazprom's grip on Europe's energy.
