Who says a PKB is necessarily "moving backwards" ?
A fixed PKB that "steals" screen real estate might be considered to be, but that doesn't mean other ways of implementing it are necessarily "moving backwards".
People are very accepting of it when it comes to computers and tablet attachments, so there really is no reason it can't be cleverly implemented in a smartphone, by bringing MORE functionality (shortcuts etc) and MORE screen real estate when typing, instead of less.
It's probably more about the size of the device, how it's carried and used. For many people, only ever used to VKB, any PKB device seems awkward, if device is used for more than just texting or emailing.
I watch the behavior of my daughters and when sending emails, important posts and replies, it becomes a MacBook task rather than iPad or iPhone task.
Agreed, they believe in compromise or need, but the solution is viewed different. Both girls independently responded that a PKB attachment on their iPad would be the preferred or at least a better solution.
My son, their brother, is ten years older, they're 14 and 16, he's 25, said the same thing when I got his first iPhone for him 11 years ago. Back then it was iPhone and laptop.
It was less about size back then but the bigger screen when the VKB slid down for media consumption. Today, my son is a senior manager in a huge freight terminal. He lugs around company laptop in a company backpack. He just bought the iPhone 9/SE2 to replace his iPhone 7 this past summer.
Happier with the added screen but didn't want any bigger. His dual carry situation on and off the job is either company or personal laptop and iPhone but no tablet. Asked me about iPad since Apple was promoting with the iPhone purchase and his sister's and I have. Even though he's got disposable income, he couldn't figure out a use case..
These are the situations facing mobile technology everyday. The compromise versus the usage and how expense is justified.
Only facts I have mixed in with opinions. I'm waiving the White Flag boon .... Not arguing, just discussing
;-)