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:
- Camera mount: as rory-alsop mentions, it would make sense for the handle to have a camera mount, so you can stick the point into the snow / ground. This blogger has a few options (among which is a tip-mount).
- Raft Paddle: the torque forces on a raft paddle are no match for a trekking pole. Even if you rigged something flat to the end, you'll bend your pole in no time. For casual paddling, you would be better off with a dead branch.
What else would you want to attach? Brainstorming, I came up with these (and alternatives):
- Tent pole extender: Some tents rely on trekking poles as their support, and as such include a sheath that extends the length.
- Saw blade (for those hard to reach branches you want to burn): Never cut branches from a standing tree. If you can't find dead and downed, you shouldn't have a fire.
- Pack hanger: Now this is something I have employed in rodent-infested areas - hanging your food bag from a trekking pole. Though in my experience, three poles wrapped together with their wrist straps does the trick - no attachment necessary (though a third pole is...)
- Komodo Dragon Deterrent: A forked stick is the preferred defense against Komodo dragons, but although a modified trekking pole might work, you are probably better off letting your local guide carry a stick he is familiar with instead of your trekking pole (and running away while he uses it).
- Dental Mirror for a Bowhead Whale: You could use a mirror attachment to inspect the rear baleen of a Bowhead Whale... other options... ummm...