i think your onto something,
i live in the south east, ive eaten dhansak from alot of takeaways locally Eastbourne, Hastings and around the south, like Clacton in Essex to London, Bournmouth and Brighton as iv'e worked away.
Dhansak is my favourite, dish it always will be.
i have never found a single piece of pineapple in any of them, although some of the menus mention it, some have had a slight flavour of it, maybe they just use pineapple juice.
the taste of the lentils coming through i think is quite important as well as a sourness, many takeaways make the dish too mild, personally i think it should be below madras in terms of hotness. after all they are described on the menu most of the time as a hot sweet and sour dish
but this variation is definitely worth ago as i love my dhansak,
i will let you know.