No, it is not as modular as the Freephone, but it is better. The Freephone doesn't have much of a choice of components - one can buy a spare camera module, for example, but one can't choose from a range of camera modules. Most people would be better served by buying an LG G2 (equivalent or better spec) and pocketing the change.
Whilst my interest is piqued by the LG G4, the choice of modules (and the concept of investing extra in just one handset, being either abondoned or locked into LG, are concerns) isn't really grabbing me. The B&O DAC would be nice, but the G2 already had a very good audio pathway, and the circumstances in which i might want to sit and listen to high quality audio don't preclude against just using a USB Audio-based solution.
Adoption of the G4 by companies (I'm thinking barcode scanners, receipt/label printers, card readers, temp probes etc) would extend the lifecycle of LG's module format, and perhaps reassure consumers that the concept they have bought into won't be dropped next year.