The Russians doing it with Kazakh oil and Gas is a bit different. The reason for that is that those pipelines are soviet pipelines built ages ago, so the infrastructure was already there, secondly Kaakhastan has an issue where it cannot sell gas to anyone outside of China directly. anything that goes west is complicated by the Caspian sea, so they don't have many ways of accounting for that, so they are forced to sell the oil and gas to Russia as there is no other buyer, they end up selling it for pennies on the dollar, then russia through its infrastructure sells it to Europe for a higher price.
The Turkmen gas swap is something similar, where Iran does not have pipelines in northwest Iran in the regions there and doesn't want to put in the money to build pipelines there, so they do a gas swap instead where turkmenistan pumps the gas to that region, and they pump the equivalent into either Azerbaijan or directly into Turkey, so the money from that sale goes to Turkmenistan.
The Iranian participation in TAPI I feel is a bit unrealistic, b/c Turkmen gas is already being used, for Iran to participate, it would have to either pump gas into Afghanistan to then be carried to Pakistan or pump gas to Turkmenistan from its own fields, but Iran isn't even willing to build pipelines to North West Iran, up to the Turkmen border for its own needs, I don't see them doing that to pump Turkmenistan with Gas.
As for the China component, that is complicated, I looked into it, and the feasibility is not all that great for Pumping gas or oil from Pakistan to China via Kashmir/Gilgit-Baltistan, the geography does not favor it and the geopolitics of the location make it undesirable for China, as the Chinese have already built pipelines from Turkmenistan and Kazakhstan as well as a 2 separate pipelines from Russia. They aren't too keen on building a redundant pipeline from Pakistan unfortunately.
The prospects for TAPI are more along the lines of exporting to Pakistan and then a potential LNG export terminal in Balochistan for the export of Turkmen gas, and a hypothetical connection to India(but that seems unlikely).
Pakistan in my opinion is better off completing the Iran Pakistan pipeline as its already doing, and just ignore whatever threats come from the US or Gulf States, you can't expect to be a sovereign state when you dance to the whims of foreign powers, jeopardizing your own strategic interests to please others, who never reciprocate. They want you to pay for higher gas via LNG rather than pay cheaper prices, all to please them and be dependent on them, when they never reciprocate with regards to sensitivities on their relationship with India, to the detriment of Pakistan.
