First of all, benefits need not be equal, but only of a sufficient magnitude so as to be un-ignorable. The alignment of economic interest must involve three basic areas: people, goods, services. The process needs to start gradually in each of these key areas, and USA involvement is needed to overcome the historical baggage between the countries, since it has sufficient clout to underwrite guarantees that will secure a steady path forward for the process.
That is exactly why US guarantees to prevent such an economic war are essential.
Pakistan must be seen by India as more than an obstacle to its desired transit routes. Indeed, getting Pakistan on board as a partner can only help India. Iran has its own issues with the US that will prevent its inclusion in any energy corridor arrangements for the foreseeable future, but that need not be an issue, because Central Asian energy resources can be routed to India via Pakistan.
This is a very good reason for Afghanistan, Pakistan and India to work together, and since it aligns US interests in containing Iran, it has a much better chance of succeeding than any idea to enable Iran's exports of energy to fund its undesirable activities.
Inclusion of Iran is an idea that will not get off the ground for the foreseeable future, unless there is drastic change in Iran, so it would be appropriate for leaders of a large part humanity not to wait for that to happen.
Thank you so much VCheng, for your well thought-out reply. And I apologize for taking such a long time to work back on it (last few days have been very taxing).
I have a few points here that make me a little less enthusiastic about the solutions offered by you.
I will write on the most grave one first:
Such deep inclusion of the US in the region may not go down well with the Chinese and the Russians. There will always be something on the line of Iran-China-Russia, because once in Afghanistan, and esp with India and Pakistan on its side, the US is guaranteed to seek greater influence further north. While walking along with the US, both the countries will have to make sure they do not turn the US into some kind of 'all immune superpower'.
Secondly, while contrary to popular belief, the US's power has grown rather than diminish in the last few years, India and Pakistan have grown way faster than the influence of the US itself. I do not see why India would not want to utilize its more powerful position against Pakistan. After all, a strong presence of India in Afghanistan is all that India is looking for - to sandwich Pakistan. What are the chances that India will not give up its gains (the ones coming from "mutual blackmail") to squeeze Pakistan?
With Saudi Arabia and Central Asia supplying all the oil to Pakistan, it can be brought to its knees in one single day at one press of the button by the US. Also, how immune will Pakistan be to its bifurcation in the name of, say something akin to WoT, when India and US both have it surrounded from all sides? - Both, India and the US will feel the need to do that no matter how cheap the transit route is, simply because once Pakistan is brought down, transit will be free.
Finally, I would like you to take a bit different approach in formulating the scenario, which I am sure you can do.
The different approach I am talking about would take into consideration the continuous efforts of all the involved nations (including Iran) trying to expand their influence. Pakistan and India, both are completely unreliable on any bilateral terms. And neither of them are trusting enough of the US. For such a scenario, that you offer, all the countries would require powers similar to the Veto in the UN.
But how much will that work, I wouldn't know, because any of the countries may decide to go for a substitute of that "mutual blackmail", and opt out at a vulnerable point leaving all other parties hanging in the air. For example, India, while getting a lot of oil and gas from Central Asia, may suddenly be offered some lucrative deal by Iran... I am dead sure India would jump at the chance of trading for oil from a non-US influenced nation!
Or say, the US wants Iran's oil too, and may even want to punish Iran till it gives in. What would be a more opportune time than this, when India and Pakistan are all for the US? All the insurgents seeping into a Shia Iran would be so well trained and facilitated it will be a chaos over there. From Jordan to Iraq to India, it will be the US everywhere, except for Iran. What would the US not give to change that? This is the main reason I strongly feel it will not be so wise to give in to such a scenario where the US is allowed such a strong, though quiet, presence in the region.
While it is still a bit vague for me how such a scenario can be designed, one thing I am very sure of is it will have to be something that can last really long because the region has been rapidly changing and would require newer grounds every other day to sustain the "mutual blackmail", and to keep it from turning into a "one-sided blackmail".