You seem to need completely redrawn sprites for each different orientation. Apart from aliasing ruining the black outlines, the red test shows a lot of lighting (which will have to be different in each orientation).
I wanted to keep the spriting work as low as possible. Software rotation was my first intention to avoid drawing the same sprite for multiple directions. The more I investigate into this topic the more I see that there is no way around it.

You might want to render small images from simple 3D models as a starting point for your sprites: they would be consistent and correctly lit, freeing you from the burden of getting the "anatomy" right.
First I thought about making 3D models and prerender them for 2D usage. My first battle ship needed 4 days to be completed. This is much to long for a single sprite. So I'm searching for a faster method/style to create the content.
Your idea of using simple 3D models sounds good. I'm going to test my performance on this one in the next few days.
Are you sure you need scaling and rotation in the first place? The video has none, and the only plausible addition that can rotate is large guided missiles (for which 8 directions probably suffice).
I'm pondering if I need rotation at all. It would be a nice feature but it bloats the asset work. Many 2D shmups don't use rotation and do well.