It is a very very interesting idea. Reminds me idea behind Fairphone - smartphone which components could be easily replaced by the user. Ask them, propose the new product…
Unfortunately trend to minimize everything made it difficult to reassemble and even recycle electronic devices.
I like modular devices and it's especially important to have more modular smatphones and laptops, for changing battery, memory or processors, but this also means device will be more expensive.
If I remember correctly Fairphone also released more than one device version, individual parts can not be exchanges between different models, and price is to expensive for specs they are offering even for older model Fairphone 3.
I could consider SeedSigner to be a modular signing device, you can buy any RaspberryPi zero model you want, print any case you want, buy and install your own compatible screen and camera.
You can replace most of parts yourself following simple instructions, and you don't have to worry someone will hack it because there is nothing you can extract.