As a Zyra main, I like this change to her passive.
But I can say it'll never be implemented because she already has another passive besides that after death skillshots, the built in CDR. I do not believe they will change her passive to what you suggested unless they take this away from her. But then again, I remember Phreak saying in a video (her champion spotlight I believe), that her design was based for a Mage that did not have to build CDR.
I just hate those games, where I end up with 2/3 deaths and feel like, oh, "Thankfully Riot gave her an after death passive. I really did use it when I was level 6 at dragon." It is counterintuitive if you go through matches without dying.
I mean, say if you are to die 5 times, and these deaths occurred at levels 6, 10, 14, 16, and 17. Her current passive is "you shoot a missle from your corpse that deals true damage scaled up with your level [80 + 20n, n = Zyra's current level]."
Sounds neat, some after death revenge. But wait, look at the levels I had died, @ 6,10,14,16,17. Assuming that these are a maximum 40 minute games. The only possible chance you can get "revenge" with her passive is at level 6 because not many champions have began stacking health (-tanks). And if you die at level 6, it's probably due to an engagement you performed as a support. So you can probably get a kill with it here.
But what about the other four levels, 10,14,16,17. Yeah, I feel it is useless. Throughout the game, if you have Zyra at a higher level, champions will have greater health as a level 16 than a level 6 unit. Past early game, this passive looses all meaning. I want something to be done about this. She is from a jungle, but does not implement this in her play style, sure her taunts do, but while snaring or knocking up opponents, it feels like you are a crazed gardener.