I think splice is risky because it lets you gain infinite value while just holding a card in your hand where it can't be interacted with. The fact that it helps you gum up the board with 1/1s and also enables its own cost reduction is ringing alarm bells for me--the closest card it reminds me of is
Sprout Swarm. Obviously this one is much less of a one-card combo since it needs other sorceries, but I still worry that in an optimized deck with enough
Spectral Procession effects it might be a little too splashy for something your opponent can't stop you from doing (unless they're playing targeted discard). It is an interesting card to think about, though, and I do think splicing Convoke onto stuff is a cool twist.
that's fair. my reasoning was that, like you say, it doesn't really scale infinitely like Sprout Swarm does because it's gated by access to other sorceries, and while you can combine token-making sorceries and card-drawing sorceries to build an engine, there aren't really any that do both at an efficient enough level to create a truly dangerous situation. but like how Sprout Swarm needed to cost 5 for a 1/1, it's very possible I undercosted this and a
splice cost would've been more appropriate. I was just comparing it to
spiritual visit and felt that even in a dedicated convoke deck, +2 to the cost for every use probably balanced out the reduction from the convoke itself. (especially since it can't do instant-speed blocker things like Visit can) definitely a card that would need some pretty thorough playtesting to get the numbers right, though.