I've had a synology since 2015. Why, besides the drives themselves, would most home labs need to upgrade?
I don't really understand the general public, or even most usages, requiring upgrade paths beyond get a new device.
By the time the need to upgrade comes, the tech stack is likely faster and you're basically just talking about gutting the PC and doing everything over again, except maybe power supply.
Understandable... Well, the bottleneck for a Proxmox Server often is RAM - sometimes CPU cores (to share between VMs). This might not be the case for a NAS-only device.
Another upgrade path is to keep the case, fans, cooling solution and only switch Mainboard, CPU and RAM.
I'm also not a huge fan of non x64 devices, because they still often require jumping through some hoops regarding boot order, external device boot or power loss struggle.
> except maybe power supply.
Modern Power MOSFETs are cheaper and more efficient. 10 Years ago 80Gold efficiency was a bit expensive and 80Bronze was common.
Today, 80Gold is cheap and common and only 80Platinum reaches into the exotic level.