In the 2nd paragraph you want to move away from China. In the 4th paragraph you want to involve China. Decide what you want.The key is Turkey. If they make the investment, they would only have done so after a careful economics feasibility of the move. Granted, it would be a small investment at first, but that is only to prevent being burned, if the politics of the venture are not right.
The central Asian countries (and Russia) would also want to diversify away from an emerging China. Which is why Turkmenistan would be the key central Asian country in this venture. They could start by building a series of pipelines for their oil and gas to Azerbaijan, as well as through Afghanistan to Pakistan and the world market. A route through Turkmenistan by road and/or rail would be all that is needed, if the Turks become interested and a secure corridor through Afghanistan can be formed. Recently Russia indicated it wanted to expand trade with Pakistan, which this corridor through Turkmenistan would do.
Western mining companies would also venture in if there is money to be made with the expected increase in demand for renewables and batteries. They may want to use this route if Biden and his incoming administration sanctions business ventures or trade with Russia directly.
It comes down to politics and if the initial investments bare any fruit. That is why a CPEC expansion through Afghanistan would be an addendum to a Turkish led effort. Chinese investors could come in to fund value added factories in Pakistan if the minerals can be shipped to them, because they wouldn’t feel as securing building those same factories in Afghanistan.
If you want Turkmenistan to ship to countries other than China look at the atlas. It borders Iran and build your transport corridor and get it over. Shipping something over the Caspian Sea to Azerbaijan and then on land to Turkey and then shipping by sea is not economical.
You are right anyway you look at it - it is either Russia or Iran or China