This unification thing is not as simple as it sounds..Do you think your other neighbors esp. Iran wont try to incorporate their farsiban brothers..Then there are Uzbeks and Turkmen. BTW most of the farsivan people i have met are not as religious as Pashtuns so im not sure how much they agree with your thought of getting together under religion.
The solution for your people lies in what your neighbors decide collectively on, else we will see another destabilization wave like 90s when there was a proxy war between Pakistan and Iran in Afghanistan.
If Afghanistan tomorrow decides they dont want to stay together or merge with a certain nation it will need some sort of mechanism unless you think someone would just capture kabul/kandhar and declare allegiance with a certain country.
Pakistan and Afghanistan can agree on common terms and put back their pakistaniyat /afghaniyat for peaceful coexistence , this can happen as a joint union like England and Scotland..but .the fence will stay in between till the danger remains.secondly think what countries wont like it, certainly the US camp/Europe wont , that gives space to Russians and Chinese to endorse such a 'unification' but if you refuse to endorse even the Russians/Chinese , they will join hands with US and make sure you fail..they wouldnt tolerate a new power center in the region like Erdogans Turkey...the difference is Turkey is a second world industrialized nation and Pakistan is third world..
This is by far the most logical and reasonable approach I've read. Afghanistan will be independent not just from the fence but simply because that's the nature of the country due to the Mountains. This approach is possible. This however is not something that will happen overnight, it will take decades upon decades until it is in the mind and interests of the people, I can see it happening if there is a war with Hindustan and the Afghanistan stands with Pakistan.


