See a bit of healthy discussion: Request - Inter Canister Calls - Add Original Caller() - #7 by skilesare
I’m still in favor of exposing almost every system variable through the msg interface(origin, block number, coinbase, etc). Having the data available only increases the kinds of systems that we build. The motoko devs generally feel differently and I appreciate their desire to keep the language simple and keep users from shooting themselves in the foot, but still…I like having the data rather than not having it.