Has there been any discussion that Trezor or other hard wallets like Ledger may offer support for ADA tokens?
Not yet. Daedalus wallet is the safest way to store your Ada so far. And I might be wrong, but I don’t think that will change due to the node being installed behind Daedalus that will allow users to stake when the Reward Era (Shelley) starts around April 2018.
I think the whole decentralisation system they are working on would not make sense anymore if everyone starts to store their ADA in cold storage.
You are correct. People not showing up for their ‘slots’ (We don’t have blocks or, at least we don’t call them that) would be a big issue. Which is why we are working on a delegation scheme. You can delegate to a delegate your stake, then not worry about anything.
In the meantime, we have the paper wallets coming out. However, for many users, it is pretty much the same as generating a wallet, writing down the seed and then deleting the keys off the hard drive; and storing the seed (12 words) in a safe.
For the pros, they may want to generate the keys on a computer that doesn’t connect to the internet. Yes, people do this kind of stuff and more. Here is a picture of me and Christian destroying a computer after a sensitive operation. We smashed and burned that thing up good.