So, that line of gadgets I have under development in my copious free time...
There's a reset circuit, which is fairly complex, and allows a single pushbutton to (a) be an input to the MCU, optionally configured as a non-maskable interrupt; (b) reset the MCU, and (c) reset the MCU and bring it up in bootloader mode to allow field firmware updates.
Given that implementing this mess in gates and one-shots would take up quite a lot of board space, not to mention being expensive, I actually implemented it in an itty-bitty MCU, specifically an ATtiny9. At 30 cents a pop in modest quantities, it's a handy solution.
Being as how ZIF sockets for programming DFN parts are hard to come by, I went with the SOT-23-6 package, even though its footprint is rather larger than the DFN would have been. I scared up a board with a SOT-23-6 ZIF socket on it, and cobbled it up as a programming fixture.
Well! Now both Digi-Key and Mouser show AVR parts in the SOT-23-6 package as limited number available, and we ain't gonna stock those no more. Great.
Microchip (which now owns the AVR line) shows the SOT parts as being available in their on-line store, with (as far as I can tell) no warnings about them being end-of-life. Hmmm.
So, maybe I should buy a couple of hundred parts in the SOT, so I can use them for the foreseeable future's production? And meanwhile look seriously for a programming socket for the DFN, and/or a supplier with a programming service for the DFN parts?
Eventually, I probably have to revise the design to use the DFN - which is yet another reason I can't use a CAD package with an expiration date*. I may, at any time during a product's lifetime, need to revise the design to replace some component that's gone unavailable. When planning for a multi-year product lifecycle, one must ensure that the tools will remain available. Lose a component and the ability to adapt, and you're SOL without a paddle.
Update: Looks like Microchip isn't giving up on the SOT-23-6 entirely; there are some PIC parts in the same package that don't appear to be EOL. Not only that, but the pinout is compatible, so I'd just have to get back up to speed on PIC (which I haven't used since maybe 1997), and adapt my (very simple) firmware. The PICs are a tad pricier than the AVRs, though. Might add 20 cents to my BOM cost in moderate volume.
* Software vendors insist that the subscription model and The Cloud are The Future. Well, I have seen the future, and it doesn't work. (I haven't seen that movie, though.)