Actually I'm not sure the full meaning of this shabad. It's very interesting that again my initial take on it is different to yours. You've read the line about paradise and heaven as pointing to people wanting that. I've read it as the Hindu and the Muslim wanting to get to their own versions of the afterlife (the particular afterlifes being the focus of the line, rather than the desire to get there). Big disclaimer, this is just my first impression: Reading more into the shabad just totally off the cuff, I think it picks up your earlier point about the Sikh version of god being 'empty' or without characteristics. You call God this name or that, but (rahao) god is the cause of causes. You both follow the peculiarities of your religion and want to arrive at your separate versions of a wonderful afterlife. But there's this reality of hukam, and if you only knew that, you'd get to the actual truth that exists behind all the trappings of two different religions that people are convinced about.