The issue in this case isn't so much Solidity, as Parity getting too fancy with their code. If you look at the wallet stub contract it's half assembly.
They did a good job optimizing the contract to use minimal gas upon deployment, but maybe that's not the best thing to optimize for contracts that will hold millions of dollars. They also don't appear to have gotten fresh external audits when they made changes.
Incidentally, there are other Ethereum languages in development that are better suited for formal verification, including Viper and Bamboo.
If I do a git clone of the parity github and deploy the multisig wallet, how much will it cost versus just using the stub/delegatecall architecture that's being used by everyone?
I haven't checked but these contracts aren't huge and gas prices are low if you don't mind waiting a couple minutes. I think you could post it for a couple bucks.
(I also think you'd be better off using a different wallet entirely; Parity's isn't the most popular anyway, especially lately.)
They did a good job optimizing the contract to use minimal gas upon deployment, but maybe that's not the best thing to optimize for contracts that will hold millions of dollars. They also don't appear to have gotten fresh external audits when they made changes.
Incidentally, there are other Ethereum languages in development that are better suited for formal verification, including Viper and Bamboo.