My old Galaxy note had a swappable battery and microSD. I don't think the rest matters. Your phone is already a swiss army knife of components and there is a whole galaxy of apps out there to make those components do cool and novel things.

Project Ara was preoccupied with having little modular blocks you can snap together, but if that's the main thing that matters to you just get some lego.

And on the other hand we get secure devices.