Broadly, I could see two situations in which people only get a phone and have no computer: either "poor" countries, where they can't afford a computer and will get a phone that's better than nothing, and very affluent ones where they'll just get a phone or tablet and not care. Although I'm not sure that this second category has no computer.
While I do sympathize with this, and I think that it would more likely than not allow people to discover this curiosity by, as you say, being fascinated with how flexible phones would be, my point is somewhat different: this isn't "going back". Phones never were open. And I'm pretty sure that the people who can't afford a computer now couldn't afford one in the 90s.
As such, for me, this is more of a lost opportunity to progress rather than a regression.