Not sure if it's something to keep forevar, but it will be an available option for a while
The reason we don't have many styles is because would slow down page loading, so we encouraged using import custom option with @import on settings instead
Kokonotsuba will soon switch to CSS Variables (something that will make teh css files more compact), so maybe that will stop being an issue and we can add moar themes without worrying about it

It's late but I added a small glow to post boxes on Mercury