The number of different block shapes we have now (full block, 3 different slabs, wedge, corner, tetra, hepta) is a massive pain in the butt for ship building and for inventory control and for manufacturing (especially when you multiply it by the number of colours, then multiply that by number armour strengths). For the current way the game works; adding 22.5 degree angles would make this much much worse - it'd be so bad that it'd be too painful to tolerate.
In my opinion; the best solution is to get rid of "explicit block shapes" entirely, and replace it with a system of full blocks and "conforming blocks". The idea is that a conforming block will auto-configure its shape to match the blocks (of the same material) that surround it; so that players can build a crude "blocky" ship out of full blocks, then add conforming blocks where necessary to get a nice smooth shape (possibly including curves).
Also in my opinion, I'd be nice if there were no colours for ship building, but there were "meta colours" instead - e.g. up to 4 "exterior colours" and up to 4 "interior colours". This would allow you to set the colour after designing a ship (e.g. set "exterior colour #1 = blue" when building a ship in the shipyard), and would allow you to repaint an existing ship after it's been built (e.g. by using/consuming paint), and would also allow the game to use a full range of colours (millions of possible colours to choose from, rather than the ~13 we have), and would reduce the number of blocks (in inventory, etc) a little more.
For rough maths, if both of these things were done, the total number of block types that player's have to put up with (for hulls/armour alone) would go from 416 down to 32. That's a massive reduction in painful clutter (with much smoother ships, with many more colours).