I think it's a nice enough idea, and I hope it sets a reasonable baseline for what enthusiast and workstation laptops will be as the entabletification of the mainstream computing device continues, but right now it's sort of a solution waiting for its problem. Economically, it doesn't make much sense for one person to buy one. In an actuarial sense, it's almost certainly better to buy something you like that's less modular, and replace it if it breaks or stops being useful for your intended tasks. Of course if no one who wishes them well buys their computers, they won't last long enough to be relevant.
Strictly speaking, just standardizing and providing the physical specifications ends up making their dongles more like headers on a desktop motherboard, potentially a commodity piece that anyone could replicate. Their other modular components seem to have a similar idea. It all seems elegant enough, and ready to "backscale" into a distributed niche industry if the big companies stop making powerful proprietary machines at the scale that keeps them cheap. As it stands, they sort of ARE de facto proprietary, but I guess the idea is that there will be enough enthusiasts, hardware hackers, and evangelists paying a sizeable, but not crippling, premium to keep them afloat and gain the mindshare to become a new standard (and hopefully halo brand) when people need to build laptops like they build towers now.