You know, I'm kind against the idea of automatic mipmap generation (e.g. through rescomp?) as you probably want to have some control over how the chunks get split (so you can decide how much trade off you want to have regarding overlap). Remember sprite limits become an issue if you start having a lot of stuff on screen.
On the other hand, I can definitely see some use for incorporating helper code for the effects in SGDK.
In other news: due to the way tiles are arranged within a sprite, manipulating the sprite width is effectively chopping the sprite (you may need to also adjust the tile ID depending which side you're chopping). This could be convenient for vertical split screen or other similar effects, since it lets you reuse the sprite graphic as-is with little effort. This doesn't work with the height (since changing it will rearrange the tiles).
Vertical split screen is definitely something SGDK could be made to easily help with.
Sik is pronounced as "seek", not as "sick".