I agree on this, wallet should really offer great security and as much as possible giving you all the control over your funds. I never heard a multiwallet that is having open source technology, the Hodler wallet is interesting.
Yes, we have to be free from trusted thrid party. We deserve a wallet that offers simplicity and security at the same time. You might consider to look at Hodler wallet in this site:
https://hodler.tech/?lang=enIt is the only multi wallet having fully open source feature.