Well, given how well keyboards (both direct hardware like TOHKBD and wirless Bluetooth) work on Jolla1 even today (it works. Everywhere where there is an edit field, the keyboard can be used, and the touch screen one minimizes) this gives very high chance for the phone.

Same can be said for Android: several official devices had keyboards (starting from the first ever HTC Dream / G1) and there hasnalways been support for keyboard and mouse into it (try plugging a powered hub into some tablet's USB-OTG and USB keyboard / mouse and see what happens). Again all the text fields work as they should. And some apps even react in an intelligent way when you start typing (in WhatsApp, in the main view (where there is no input box) when you start typing, you automatically get a quicksearch box).

This last one brings us to the potential improvements on SFOS.

Don't get me wrong, Chen's device could already be shipped like this and be working.

But there's a lot of potential improvements. Currently SFOS is mainly a touch only system. When there is no input field in focus, a keyboard currently no further use.

Later updates on SFOS could also include intelligent things that the keyboard could do when no input field is in focus. E.g.:
- like the Android WhatsApp exemple above: when the display is a list, keypresses could help search around (this could help a lot with pull down menus on web pages. As their order is random, currently even SFOS "scrollbar with letter book marks" can't be used).

- like the "Just type" functionality on HP/Palm 's webOS. On the main app view with the app-cards, if you start typing you'll get automatic suggestion of anything: starting apps whose name matches your input, contacts, etc. Or even start specific actions: search the web with you input, start a note, etc. User-installed apps could provide their own pluggins for this feature (installed 3rd party map apps could provide a search actions)
Most of the interaction can be started by "Just" starting to type, and then clicking on one of the suggested quick-search results or quick actions.
(E.g.: just type "cam" and you'll get suggestions of starting the Camera app, quick search results of contacts called "Camille" or "Carol Meier", or search Wikipedia with keyword "cam")

- Palm's older PalmOS had base apps react on keypresses if you started Graffitying with the stylus or typing on external keyboard : the note taking app would automatically open a new note for you to write, the calendar app would start a new entry, or if the typed caracter was a number, start setting the time of this new entry.


So there's a lot of room for improving things even better.
But base functionality is already there.

And in my humble opinion it would be best to ship the device fast to get it into as many hands possible - even if there mostly input-field onoy support.
And subsequently improve the support in updates (keyboard uses outside of input fields).

Tha would give the possibility of motivated 3rd parties to also improve the support (some genius might write a "Just type" like functionality)