Just for giggles, I tried plugging a USB keyboard into my phone via an OTG cable, and wonder of wonders it worked. The catch, of course, is that you'll eat your battery by powering external devices, and the keyboard dwarfs the phone. A Bluetooth keyboard would probably be a better bet for anything but rare use, and there are mini BT keyboards that would be easier to carry.

Too bad built-in slider keyboards went the way of the dodo. There are times when the extra screen real estate from not needing an on-screen keyboard can really come in handy (and Termux is one of them).