Although I agree that this would be a great feature, I suspect the amount of work it would take to implement would be significant. The problem is that the user’s preferences would need to be accessible by the push service, which is only possible in the following ways:
1. Give push service access to the wordpress database. Really not a good idea from a security standpoint, especially considering that the push service might be on a physically separate machine, and so securing the connection will be a lot of work.
2. Store the user’s preferences on the push server rather than the wordpress install. This could get very messy, as these preferences would need to be updated every time for example that a new category is added to wordpress.
3. Have the plugin send a list of registered users to push to when it sends a notification request. This is probably the most feasible option, but I can’t think of a good way to implement it for sites with a large number of registered users- bear in mind that this would need to send a list of _all_ registered users, not just the ones that are subscribed to push, which wordpress has no knowledge of
For now, if you would consider it useful, I could certainly modify the plugin to send the category id when it makes the request to the push service (although you would need to modify the push service yourself to actually do something useful with that data).
