<p>I now own the Prusa3D MMU2.  The benefits, costs, and experience others have had is well documented.  I am interested in rebuilding my large, home-designed delta machine to be multi-material, and don't want to overlook strategies I haven't considered.</p>

<p>My original implementation used an E3D Kraken as the hot-end, and handled the inevitable delta tilt by adding two additional degrees of freedom to the head to lower the selected nozzle to the bed.  I've been through three generations of mechanisms, and I think the third will work.</p>

<p>But, I feel that I am not seeing obvious and better alternatives.</p>

<p>So, the question:  Through what methods and mechanisms can a multi-material (different polymers, different temperatures) FDM printer operate, and are there available designs or examples of best practices for those methods?</p>

One of the easiest ways that I've seen, which I'm a fan of, is simply putting Y splitters on your Bowden tube and having multiple feeds to a single hot end. The main benefit is that you only need a single hot end, so you don't have to worry about extruder offset or alignment or anything like that, but you do have to worry about material blending somewhat. Basically you end up needing to build a "purge tower" next to your printed items that you use to transition from one material to another.
There's the Diamond hotend setup that basically moves the connections into the hotend itself, which reduces the size of your purge tower but increases the risk of burning if you're trying to print with materials with vastly different printing temps, like PLA and PETG.
You could also have swappable hotends but that requires you to be there to manually swap the print head twice per layer. Don't recommend.
Unfortunately there's only so many solutions to the multi material problem, either you put multiple materials through a single hotend, or you have multiple hotends. I'm a fan of the single hotend approach personally, especially on deltas where weight and space are at a premium and alignment becomes problematic.