It can be formed if the narrative is anchored in the geography and history of the people who live there. This is what France, Germany, Turkey did. If France had gone for "Christianity" then today every Christian would have been a putative French.The thing is Pakistans nationalism can be developed due to history, culture and religion.
95% of Pakistani's belong to broadly five ethnic groups [something analogous to UK with it's four nations with their flags meshed to form the Union Jack] who live in the five regions of Pakistan.
These peoples have evolved around the Indus River over 8,000 years going back to the ancient Indus Valley civilizations. Pakistan is just a modern label for a very ancient land. This all makes for a very distinct and unique national project. No doubt Islam had a had impact like it has on so many other peoples. The mistake Pakistani el;ites made was just emphasise Islam and ignore or even discourage our own ethnic histories.