The Pashtun ethnicity should not be a border but a bridge between both countries, and I think that there should be large-scale initiatives on govt. level (like naturalizing the 1000s of Afghan refugees who are already integrated into the national landscape - an entrepreneurial group - but want to be full-fledged citizens of the country), but this "Pashtun is Afghan and Afghan is Pashtun" mantra used by some "nationalists" in fact won't pose a problem to others ethnicities of Pak, but to Afghans first : tell that to a Tajik, an Uzbek or, especially, an Hazara. That's what the Hazaras went through because of the Pashtun dominance :
http://www.refworld.org/cgi-bin/texis/vtx/rwmain?docid=49749d693d
You have to keep in mind that Pashtuns are 45% of Afghanistan, while others put together make the rest : there's a demographic balance which keeps Pashtuns politically and economically in-check. Punjabis, Sindhis or Muhajirs don't have a historical problem with Pashtuns, the proof being that the largest Pashtun city nowadays isn't Kandahar or Peshawar, but Karachi (which hasn't traditionally been Pashtun at all, but nowadays hosts 1000s of Afghans) ; when it comes to Hazaras, Tajiks and Uzbeks, though, they wouldn't want an additional 35 millions Pashtuns from Pak adding to the 15 millions already present in Afghanistan, who would then keep bullying others for their "Afghan = Pashtun = Afghan" ideology.
Indeed, Pashtuns are evenly represented in the armed forces (same as their national pop.), while Punjabis are slightly over-represented (nowadays around 55%, once it was +80% !) but Muhajirs are the most over-represented (17% come from Sindh, while the majority of these Sindhis are in fact Muhajirs from Karachi.)
