Making a device that transforms any keyboard to bluetooth has been discussed on many forums. We designed a bespoke battery powered module which relays any keyboard HID code through bluetooth to another device.
The product uses an ARM M4F processor within a Nordic Semiconductor SoC which is compatible to transmit using the latest Bluetooth v5 protocol. Additionally the firmware can be modified to allow connectivity of any HID capable device.
After community feedback the device is being redesigned for a smaller form factor and it is expected to launch mid-2018.