So one thing that people never think of using scripting for is visual effects. There's simple linear effects like sliding windows, hp bars that take time to go down, etc. There are also spring effects, which are generally smoother, and used in newer games. I've implemented a short (less than 50 lines) little physics engine in RMXP that could be used to create these effects, and others. It is completely lag free, it just runs a few calculations in the background when being used.
Now, on to the point of this thread: do you want me to build in support for particle effects? They look nice, and all the new 2D games use them (flash, XBOX live arcade, etc.). I don't know how well RMXP handles changing sprites, but obviously, if it lags we will scrap it. Any opinions?