Can't predict the future so it's very hard to tell. Looking at history doesn't predict the future.
I guess you're at mercy of developer interest as long as the hardware itself has the storage and ram you need? Or you become the developer/ hardware hacker yourself.
If you don't care about >100mbit. Then pretty much any AP/switch/router will do in terms of performance? So AP stick with DIR882 until required?
We just need to advise on a router you won't have to mess with as often? Given you can run many AP's, that part of the transition when required is less error prone? i.e. Can leave the old AP on when setting up the new AP.
Buying new is challenging to keep in budget and have an easily flashed device it looks like. It also depends on whether you're willing to compromise on power consumption/heat dissipation too.
I'm in the x86 mini PC camp for the router. Or a "popular" single board computer?
You could also compromise on dual NIC and get a managed switch if you can find a cheaper single nic device. For example used thin client/ tiny pc.
Then AP of your choice you upgrade as required.
For router The RT3200/linksys e8450 is going to require messing with flash partitions again to move to 24.x due to ubi changes? Similarly HiveAP 330 required bootloader flash modifications for 22 to 23. So that's an issue sometimes depending on what gear you get.
Stuff on what I run, my old gear that lasted a while, notes on long term support in terms of hardware
Notes on what I do myself:
At an SMB site I run the x86 router + managed PoE switch + many older PoE AP's running openwrt as I can compromise on power consumption there for uptime and ease of configuration/migration.
At home it's basically the cheapest ARM router for primary. And cheapest 2x2 or better AP's. To simplify configuration I splurged on the cheapest DSA compatible AP's as my existing mt7628's were running out of flash and memory. But I could do it one AP at a time, test and then decommission the old one. Without causing issues for my users.
Personally I'm thinking of moving to something like the new to openwrt, fortinet fortigate stuff. As it has 2GB ram, USB port, and the 51/52 look like they have external storage too. Plus USB port and serial console.
My anecdote on old gear:
I've got a very very long time out of my DGND3700v1 for example.
I'm very happy with my run of ath79 ap's and devices which had ath9k cards. My ath79 gear is running out of CPU, whilst my mpc85xx stuff, except for sometimes lacking packages being built for it by default still has enough CPU performance for what i need. But you still get >100mbit wifi which i would argue is fine for normal internet use.
Regarding long term support:
In dreamland, I'd lean towards something that has long term device support from the manufacturer. i.e. they'll sell it for the next 10-15 years. It's even better if they already provide full source, upstream stuff and third parties base their designs on the reference design from a manufacturer? Plus socketed WLAN =P That's pretty hard to come by. (makes me think Microchip/Microsemi/NXP, but they requrie you to sign in and ask for sample for linux source?) Hence x86 for routers. Or be willing to upgrade a bit more, or compromise if you need an all in one device.
