Under file it should have "Write offline transaction" and "Put offline transaction online" or something along those words. Already has sign/verify message, sweet feature.
bitcoin-core is 99% about protecting the network by decentralising the blockchain.. so features will be a secondary thing.
much like banks SWIFT network has nothing to do with Visa's contactless NFC features.
but if you want the feature added to bitcoin-core, there is nothing stopping you talking to the dev team.. as im pretty sure that comments on this forum dont really register on the dev teams radar as a place to get feature requests..
plus because it's not really essential to the security of the network, maybe a donation to pay for their time would sway them to divert resources away from security and onto user-friendly.
But you can't fall under the trap of keeping Bitcoin Core as a super limited software with basic features forever if you want to give people an incentive to run full nodes. Sure, it should stay basic and extremely solid, but make it more usable and user friendly as well.