Voice-interfaced intelligent agents like Siri/Alexa/etc will continue to evolve.
Given a sufficiently advanced AI, buttons won't be needed for most computing tasks - any more than stirrups and a bridle were needed to drive the first automobiles.
They will connect to our brains.
> or fit a camera lens, or speakers, > or a large enough screen in there.
Not needed when they are connected to our brains.
Meanwhile, non invasive BCI are getting AWESOME...if you are a quadriplegic with no other options.
Now imagine we solve those problems, and the first BCI is on the market. It's safe, it's a little bit faster than typing/reading (hey, first generation right). Who is going to be the first early adopter to undergo massive brainsurgery? Turns out upgarding cochlear implants is so hard they are made to last 100 years (they get surrounded by bones and scar tissue...) so upgrading will be really hard. And who wouldn't want to have their blackberry implanted into their head right now...even worse, if we have proprietary technology in the first ones and now your brainberry can only talk to other brainberries...or we go full internet of shit and it needs a cloud server to do anything:)
You'll be needing an oxygenated brain for when they arrive.
"Mainframes, minicomputers, desktop personal computers, laptops, and now tablets and smartphones" -- yes, so we had like 5 generations of computing hardware platforms. And we began with so premature and begging for improvement technologies (when they started in the 50s) and so large form factors that we had Moore's law going on for decades until a few years past.
Now we've reaching physical limits in CPU shrinking, and we have components so small (e.g. Apple Watch) than if they were any smaller you couldn't handle their buttons, or fit a camera lens, or speakers, or a large enough screen in there.
My point is, just because something has been going on for 5 generations of form factors, it's nowhere near enough evidence to be meaningful statistically or otherwise to deduce it will go on forever.
A turkey is fed every day by the farmer for months on end. But after 300+ observations that make it think feeding is never ending and inevitable there comes thanksgiving.