I take the point about the profile usage and will pass that on to Steve who created the BP integration plugin. One of the important things against doing something like this is that as soon as you do then you create a lot of code overhead that has to be loaded on every page of your website. This is true of all template tags, widgets etc., that any plugin supplies of course. We try very hard to be as light as possible on non-forum views.
However, on the subject of the subscription – can you not turn on the admin option to auto-subscribe your members to all topics they post to? Or is the objection to that that they do not get to see or use the SP profile therefore can not turn it off again?
As to “list all the topics by XXXX user” can you expand on this? Are you suggesting that a member can nominate another user to see all of their topics? Posts? Do you mean their own?