Unfortunately, this has a lot of drawbacks. Amending the constitution requires a 60% supermajority, which I think is appropriate for constitutional questions, but is too high of a threshold for ordinary policy legislation. In this case, repealing the laws against abortion and marijuana have majority public support by a wide margin, so why should we have to pass new constitutional amendments with a 60% supermajority just to repeal bad statutes that were passed via the ordinary legislative process in the first place?
On top of that, because measures passed this way become constitutional provisions, rather than normal legislation, it makes it difficult for the courts to exercise judicial review and reconcile these measures with extant law. It's sort of the worst of both worlds.
Maybe we should try to get an actual ballot initiative process into a draft constitutional amendment for the next election cycle.