The goal would be to have that kind of developer-friendly functionality in a much more powerful and usable form. Imagine having a "phone" with a robust and developer-friendly OS that could wirelessly connect to external displays and peripherals. You'd have a single, compact brick of computing power in your pocket at all times. And if the oft-projected future of cloud services comes to fruition, the device itself wouldn't necessarily have to have ultra high-end computing power or storage.
That's a mobile experience that I'd get excited for.
Go for an HP graphing calculator, then. ARM processor, SD slot, far more powerful programming tools, especially the built-in ones. TI's have BASIC on the calculator, but HPs have an interpreted language, a compiled systems programming language, and an assembler and disassembler all in ROM. And you can run a C cross-compiler on your laptop.
It's nowhere near as powerful as a PDA, but it has a great keyboard (for math, at least) and runs off AAs.
I learned assembly on the MC68000 in the TI-89
Oh yeah, the BASIC on those TI calcs!
I spent every calculus class working on various things. My proudest accomplishment was a blackjack game. I implemented drawing routines for every card type, which was really painful given the graphics primitives you had available. So much Line(..) and PxOn(..).
Distribution mechanism was hooking up that cable to your classmates' TI-XX. Maybe iPhone devs should try that.
Much of my free time in highschool was spent creating games on it. It's extremely easy to develop for (it uses a variant of BASIC), and the menu system is designed to minimize keystrokes, which means you can bang out your code very quickly.
Of course, the platform is very dated: 6 MHz CPU, and a 96×64 monochrome LCD screen! I'd love to see something in the same format, built with modern technology. Maybe the default language could be Python.