I quite like the concept, however given plugins are written by all and sundry, without some sort of schema which defines what weight to choose, for your plugin, I fear that chaos might ensue. If we could have weights from 0 - 10 with the default at 5, that might be simpler.

However, in most cases it probably doesn't matter which order plugins are run so this just seems a little too sophisticated a solution for what is a basic requirement. 

That said, it might be useful to have High, Normal and Low priorities.