3D printed bike

That lug set above is by Metier bikes. Jamie White wrote this about titanium printed lugs (for bonded carbon frames)....

The advantages of 3D printing lugs rather than machining them are:

1. You can design features that are impossible to machine.
   complex internal cable runs, integrated cable stops, brake mounts, cutouts to minimise weight &
   internal sleeves so that the carbon tubes are bonded on both inside and outside.*
   
2. Zero waste.
   The Ti powder in the print bed that does not get made into the part is reused.
   
3. Complete customization.
   I use complex cutouts and patterns that look nice (I think) and lighten the lugs.
   I can rapidly accommodate new industry “standards” ( 148mm rear hubs, dual-mount Shimano road brakes (like on the Trek Émonde)
   I can modify standards for a particular purpose, e.g. putting a custom Syntace-derived derailleur hangar on a gravel bike.
   
   

The disadvantages of 3D printing lugs are cost and tolerances:

1. 3D printed Ti lugs are expensive, and so only make sense on one-off, fully custom boutique bicycles and you won’t see them on production bicycles for a few years
   To compare printed and machined/welded lugs for Ti/carbon frames, Ballpark is currently $10k USD for a Metier frame vs. $6,500 for a Firefly Carbon-Ti
   
2. The tolerances on 3D printed parts are way worse than on machined parts.
   I get around this problem by designing the Ti parts a little bit proud and reaming them or hand-finishing them to machined tolerances, depending on the joint.
   
   

If you're then comparing full carbon custom frames with C-Ti lugged....
The advantage of Ti lugs is that C-Ti frames can be easily repaired:
joints can be unbonded to replace a damaged tube. You race, you crash: If you’ve ever cracked a carbon frame and had to send it off for repair, you can appreciate a fast, easy repair.
I keep standard tubes on-hand for quick repairs. Depending on your point of view, repairability might be part of “sustainability”.