User blog comment:JustSomeDude.../Law's Plan & The Shichibukai/@comment-5962458-20130202180611

I think his ultimate plan is as simple as stated in an earlier chapter.He just wants to mess things up for the current great powers of the world so that the new era of younger dreamers/pirates can emerge.By defecting D.D. he wants to weaken the sichibukai, by defeating Kaido he wants to weaken the yonko.I don't know his plan for the marines but i guess having to deal with D.D. and his underworld connections would solely be a huge hinderance for them as well.

So my point is that there is no single ultimate plan he just has figured some means to deconstract the world as it stands at this moment and for the last 10 years or so.