Can anyone point to any commercial or DIY trekking poles whose end-piece can be swapped -- i.e. regular pole point, sharp spear, raft paddle, camera screw, etc?
I would wager that such a thing does not exist. Of the attachments you mention, only one (sharp spear) seems practical. Issues with the others:
What else would you want to attach? Brainstorming, I came up with these (and alternatives):