Not that my word as an application dev means much since I'm not a protocol dev, but from what I can tell the main downsides would just be the small complexity increase with new opcodes and the standard unknown unkonwns from deploying something new on a public network.
Bitcoin code is extremely conservative with OP_CTV being relatively few lines of code with years and years of scrutiny put into it.
We'll likely add a few things with OP_CTV such as OP_Vault to make sure there's enough benefits vs risk when the upgrade finally comes.
There is a ton of info available already on these two sites, please check them out and DYOR: