I went back to using a ThinkPad from 2012

I've used an X200 for ten years (I bought it used with 3 years on the clock) and I'm actually surprised that the X200 is kind of glorified nowadays as one of the best Thinkpads ever, because back then the X200 was decried for its numerous build quality issues (palmrest, right half of the keyboard, thermals, noise etc.). The X200 is of course build fairly well compared to the more recent models, but that's hardly surprising. From my PoV the Thinkpad series has been constantly and consistently reducing build quality for at least 15 years.

(That being said most of the issues the X200 has had were just things that feel poorly, it won't fall apart)

I've done the same only with a T440p.

Upgraded everything (cpu to 4 core to 47w model, max ram, CD replaced for SATA bay, screen to 1080p, touchpad to T450 version), even updated the bios to a modified version so I could set my own power curve parameters. Works great most of the time though the screen I got has deteriorated and needs replacement. I'm going to replace the fan as well as the bearing is giving out but it's not high speed on most of the time anyway.

Had a T430 before that with the same upgrades but that motherboard died.

For Thinkpads, T450 (from 2015) probably hits the sweet spot as a daily driver. Few important notes:

* Haswell got most of the major ISA extensions like e.g. AVX2

* T440 did not have buttons for Trackpoint, making it pretty awful

* 802.11ac 5GHz wifi and USB 3 are nice to have

I think comparing old desktop with new laptop is going to give you different experience than comparing old laptop with new laptop.

I got M1 Air and not only is it a huge difference from my previous 2017 MPB 13" (which I gave to my mother who spilled coffee into her previous laptop), it is much better than my work provided 2019 MBP 16".

"Snappiness" is subjective and hard to measure, but the thermals are huge difference. My work MBP is sitting at 63°C with just Firefox pointed at HN. On both my old MBP and the work one, playing 1440p video (native screen resolution) would make it loud, and playing 4k video on 4k monitor would turn it into a vacuum cleaner.

The Air is completely silent at all times (it has no fan) and sits at 32°C while playing 1440p and maybe 40°C when playing 4k content.

It is of course possible, that this is all because the previous Macbooks were so bad (and due to hw decoding for common video formats) but I had similar "Jesus this is such a loud, overheating mess" experience with other laptops as well. But desktops have much better thermals already - so for you, the biggest difference would be the mobility I guess.

Even assuming Framework shuts down tomorrow and destroys their existing stock of replacement parts and the specs for making new ones, I would argue that you can at the very least assume permanent availability of RAM, SSD, Display (it uses a commodity panel), fan, and battery (there are knockoff batteries for much more obscure laptops).

I would assume that keyboards, trackpads, etc. will also be available as some laptops bite the dust and are scavenged for parts.

Whether the motherboard/CPU will actually be upgradeable obviously remains to be seen. The 11th Gen CPUs get a lot of flak, but they have good single-core performance which will make them suitable for general use for a long time.

It's at least equally upgradeable as the first ThinkPads with soldered on CPUs, which by today's standards is still pretty good - and if framework deliver on their promises, then it will be even better. But either way the baseline isn't bad.