There's different options for different things.

You have:

- EEPROM for low/medium frequency of update, small size, persistence

- NAND flash for low/medium frequency of update, semi-arbitrary size, persistence

- eDRAM variants (Mosys '1T SRAM' comes to mind, which is still DRAM but has more dedicated Row/Column circuitry vs SDRAM's RAS-CAS timing shenanigans) for frequent update, volatile or maybe battery backed storage, non-persistent

Which... we -kinda- see in some layers already, as eDRAM has gone from 'fancy server procs and halo mobile chips' to a -little- more mainstream.

Not really, no. For a start, I don't think NAND flash itself is an example of planned obsolescence: its main predecessor is spinning rust platters, which were notorious for sudden catastrophic failures. Spinning rust replaced, more or less, magnetic tape, which does have an effectively unlimited lifespan (it's more likely that you won't find a working tape reader than that you'll find properly stored tape is no longer readable) but is otherwise a terrible storage medium.

But more on point, this article's context is static ram on-die for a microcontroller or similar. One possible replacement for SRAM is magneto-resistive RAM (MRAM) - it's not quite as fast as SRAM but close enough for many applications, it's higher density than SRAM, so it'll take up less die space, and it's non-volatile so µCs can ditch the NOR flash often used for code storage.

One great thing about MRAM is that it has no write wearing: it has an effectively unlimited lifespan, without all the downsides of magnetic tape. I look forward to seeing it (or similar technologies) in microcontrollers in the future.

Magnetic tape doesn't have unlimited lifespan. You can store it almost indefinitely, but reading and writing tape will cause quite a bit of wear and tear on the media. But yes, it would be great if MRAM turned out to have such a favorable profile.

I remember hearing about MRAM while I was studying Materials Engineering at uni, also mentioned was Phase change memory, which worked off of a phase change between Crystalline and amorphous states in a glass material did anything ever progress with this technology? It sounded super interesting at the time.

I'm very far from an expert in this field, sorry. PCM (and other resistive memories) are definitely still a thing, though - they've been used for in-memory computation, doing vector-matrix multiplications directly in the memory cells and thus saving massive amounts of die area over using separate CMOS logic, so they're probably going to replace on-die SRAM for some applications.