I’m more about going small, portable and cheap, rather than exotic. I don’t see the point of using very expensive (and heavy) rods when my whole design ethos is about simplicity and weight reduction. Ideally I would use carbon fibre rods for XY. If they end up being disposable after a certain amount of time, I can live with that, as long as the design makes that easy to do.
But, ideally I would use some sort of bearing surface that doesn’t eat the CF tube - like PTFE tubing, for example.
Materials technology is advancing faster than my ability to read about it, but sticking to ‘tried and true’ isn’t my bag.
If I am going to design a machine to use CNC cut MDF components, I want it to be small and light and cheap. The biggest problem I see with 3D printers (especially DIY and kitsets) is in getting things square - something the CNC makes a piece of piss. Using off-the-shelf components like pulleys from embroidery machines (CHEAP!), regular sealed bearings, external laptop-style power supplies, accurate extruders and heads of a well-accepted and supportable design is where I am at.