This is isn’t really a concern for me because firstly eve is highly motivated by community preference so I would feel really comfortable buying into eves ecosystem without fear of being ripped off or ignored (as Apple routinely does)
Second as you rightly said Eve can sell ‘empty’ modules. That’s essentially what the GPU module is. A hard drive module can be a similar empty box with two 2.5 inch drive bays. They could sell an emtpy PC module compatible with Mini ITX boards (the module would have to be 180 x 180). Or maybe a barbies version like a skullcanyon NUC .
Also most components that are part of the system are generic parts, only the specs really matter not the brand behind them like; hdd’s, ssd’s, blu ray drives, speakers, network switch, TV tuner and so on. And we get to choose/vote for the competent specs.
So it’s a win win clean desk with preferred components, future upgradablility all in a simple customisable form factor.