That's a great comment not just for this, but for all proposals!
In this case, one main risk is on the user experience side. Migrations always add confusion. We hope doing it in steps, combined with communication is enough. Also doing it in this environment (with low general activity) is better than in the middle of a bull run.
Another one is the increased exposure to ETH. We do cover it in the text above (I hope/think).
Platform risk, also somewhat covered above. Balancer is battle tested, but not the same TVL or time alive as Sushi.