Safaricom is partly owned by the government (Kenya). I would bet hell would freeze over before Safaricom would give a Bitcoin wallet provider access to their local USSD gateways (which are required for secure communication of mobile-originated requests.)
Right now most new phones sold are smartphones. This still means only a small segment of the population ... (like less than 20%) has a smartphone today but that's not as huge a hurdle as it may seem. Families and neighbors are used to sharing resources. Those that don't have a feature phone even yet today might have their own SIM card though. With this SIM card one can borrow a phone to use M-Pesa, for example. With an inexpensive hardware 2FA device a person without a smartphone can safely borrow someone else's smartphone to make a Bitcoin transaction. Even paper-based wallet using BIP-38 might be useful with a borrowed phone (one that is provided by the merchant even), presuming the password is single-use (i.e., spend all funds in that wallet and the wallet is not re-used).