definately a good starting point! but i think we need to be able to adjust some things to make good use of the official sprite font plugin and the output of your tool. what about power of two textures and more control on positioning the chars?
the thing is that bitmap fonts are a great way to bring customized / styled fonts to a game and not just a prerendered ttf/otf/etc.. but currently i dont really see a good way with the official sprite font plugin to accomplish that.
anyways.. thanks for your tool! maybe you find the time so adjust some more features to better work with the input sprite sheets.