3D printing a set of hubs (or what ever I think of)

That's gonna snag shorts.

im gunna prototype, then if this is a problem ill alter the design. although im not that acrobatic on my bike.

How about exploiting the gap so the bottle approaches from the side of the bike? Fewer tyre clearance issues (or toptube issues for this with the bolt at the front)

theres actually a company that tried to kickstart this design:

http://www.swarmeffect.com/designs/seatclamp

It was actually successful, but they arent producing them anymore :(.

its actually quite a hard design challenge because a bottle opener is quite large relative to a seat post clamp. the bottle cant be sideways either. plus, both CNC and SLS must be capable of manufacturing the thing. my mark 2 design cant actually be CNC'd. Which is a massive fail on my behalf because it easily could have been, and missing this also makes it much more likely to fail.