I do agree with you that it is important to have physical controls rather than only touchscreen controls.I am a fan of iBasso's DX100, but it drives me crazy that one has to pull it out of one's pocket every time one wants to change the track etc.
I think it may be particularly an issue for DAPs produced by small companies, that rely upon Android as the operating system for the DAP. It obviously requires extra money and research to develop a 'layer' to facilitate the function of hardware buttons that interact with the Android OS in spite of the touchscreen being 'locked'.
Cheaper DAPs like Cowon's J3 have wonderful simple-but-effective hardware buttons for their proprietary operating systems, yet expensive DAPs like the DX100 are awful to use (the DX100 sounds fabulous though, so, in spite of it's shortcomings, I do still like it).
Like you, I really hope Calyx don't take the shortcut of not bothering to include hardware control buttons on their DAP.