Only it's not outdated because Apple just re-released a new 7th gen iPod Touch this year with the exact same screen. So developers are still going to be expected to support it for the next few years, at least.
I understand how you could think that 4.7" isn't much bigger than 4", but remember it's measured on the diagonal — and all the 6/6s/7/8 phones have a thick bezel around that larger display, making it much too big for comfortable one-handed use...you have to do the dreadfully one-hand-shimmy up and down the phone to reach the full screen. I "upgraded" from a 6 to an SE solely because I didn't like the size of the 6. Perhaps a 4.7" screen would be manageable for one-handed use *if* it had no bezels, but Apple has yet to release a form factor like that.
Yes, but they won't. I don't see it coming, sorry. It's very likely that Apple won't do another compact 4" phone (SE-like design) or an all-screen no-bezel variant of the SE with 4.7" because there is almost no market for it. They need to develop such a phone and have the tooling done and prototypes and research and development and on and on...
Most of the customers are fine with the current set of 4.7" - 6.5" phones. I know, many others are desperate for another compact SE-like phone, but there is simply not market for it. The SE released 3,5 years ago. And no real successor until this day. Why is that? Because the demand for such small phones decreased rapidly over the years. Otherwise Apple would have already given you that SE successor.
Apple would need to sell millions of units. iPhone 6s and 6s Plus were more popular than the 5s/SE in 2015/2016.
The iPhone 5/5s/SE time is over. I'll highly doubt phones like that come back. Look at the Android phones. Every serious Android phone i know has atleast 5" of display, with or without the bezel. No matter the price range, from 200$ to 1000 $.
And honestly, an iPhone 6/6s/7/8 isn't too bad. You can get used to that. I had my 6s for 3 years and i could hold and use that phone with one hand just fine. Yes it's a bit larger, but it works.
And for the iPod touch, Apple had to update that. The 7th gen is literally the same device as the 6th gen which released over 4 years ago, and the only difference between the 6th and 7th gen is the A10 chip, 2 GB of RAM and a 256 GB option. Same display, same camera, same colors. Why did they update the iPod touch? Because of iOS 13. They had to.
The previous 6th gen iPod is not able to run iOS 13 (same as the iPhone 6), because they only feature 1 GB of RAM. Apple doesn't care about the iPod touch anymore, neither do they focus on it. But because some people still buy it i guess (it's a great secondary device / music player for the gym or for your car or for the kids) they wanted to keep it in the line-up (it's under Accessories btw on Apple's webpage).
Maybe they expect developers to make Apps and Games for the iPod or for the SE (SE is supported by iOS 13 after all), but many noticed that some apps (even stock apps) feel kinda cramped. iOS 13 is not made for such a small screen. iOS 13 will support devices with 4", 4.7", 5.5", 6.1" and 6.5" of display. And they need to scale all the apps for that.