Beam is incorporating a BBS system that presumably could be used for secure communications as well (ow how could it be secure for setting up a tx?).

Won't Grin have to do something similar that would support secure messaging in order for users to build txs in a secure and easy way?

I'd say if u can send Grin via email/mobile easily cause of no scripting and it is truly digital cash that is private censoroship-resistant/decentralized p2p distributed ledger then this is big