quoth smileboom's Twitter account: "We are preparing an update of SmileBASIC along with the JP version. We cannot tell a firm date for the overseas yet but it is coming in Apr. 6:54 p.m. - 28 Mar 2016" Got myself excited for an EU release for a second there. Updates are good though!

Any idea on what they're adding? Just stability or any actual new features?

Many, many wonderful new features, such as a built in BIN$ function (always thought that would be good since PTC). There's also new sound things (which I think are actually DLC), clipboard access, different size BG tiles, higher-precision version of MAINCNT, etc. SmileBASIC Source's "So what do we know about SmileBASIC 3.3?" forum is the best source to find out more.

This better not change anything! I just learned how to place and locate a sprite or load a custom file! I dont need any changes.

New version keeps upper compatibility, then the knowledge which you've learned in current version won't be a waste. The only thing which I get a little worried is stability. Modification sometimes causes troubles.