Many of these types of ideas are to use an easily compostable material and mix it into the plastics as a filler or add tons of binders. The most common 3d printing plastic PLA, is technically biodegradable but will only undergo sufficiently rapid degradation in industrial composters which have elevated temperatures. I was investigating using cellulose acetate based filament but it seems there are still quite a few issues with what I was able to find in the literature (low flexibility and brittle, additives can interfere with biodegradability). Some proposed methods use other plastics that seem to respond well when mixed with cellulose and the same plasticizers but I haven't seen much other literature focusing on making cellulose based (as the main polymer, not as an additive) filament (not printed dissolved in a solvent as a gel and then dried).

https://www.youtube.com/watch?v=jCsnVp6mEbk

As for this method, if using binders that are easily and cheaply made, and are biodegradable, then I see no issue other than needing to use specialized printers. TBH I wouldn't mind prints which can't withstand being dipped in water because most prints probably aren't being wetted anyways.