Bloody hell...only 2 hours ago I was just thinking of something similar (well, ok - not QUITE the same, but I like the idea of this one!) HEY - just think if you did the whole "grafting" thing like they do to get pears growing on apple trees and stuff with it...hell, just think of the CLONES you could get from topping like that! Top once then you get 2 main stems which you can LST, then top/take a clone from the end of the 2 branches, THEN all the budsites grow up towards the light, more clones, etc.
God I just thought of/realised that one...ok, I know everyone already knows about it but it could work bloody brilliantly if you had the space (I took clones about a month ago just before flowering and now I've got a 2-prong fork instead of a single one...my only time topping I screwed up - glad to see I can ACTUALLY get it to work!) - having said that, with only 1 plant and root ball being kept alive for god-knows how long, it'd be a HELLUVA loss if you effed it up!