The COCONUT proposal aims at the definition, study and realization of a new fully scalable optical access network significantly extending the network dimensions in terms of bandwidth utilization, reach and number of accommodated users. The envisioned access network evolves from the almost-commercial WDM-PON architecture to the realisation of the Ultra-Dense WDM solutions, opening the way to the "wavelength-to-the-user" concept. The key enabling technology will be a new cost-effective coherent detection scheme. This will allow for the first time to leverage from well known concepts to implement really cheap, yet effective, coherent terminals suitable for mass deployment. Although conceptually complex, these terminals must be compatible with the cost levels typical of low-cost consumer electronics, thus affordable to the end-users. Therefore COCONUT can drive the realization of flexible and bandwidth-efficient next-generation networks, compatible with the existing PON infrastructures. As a result, high speed connections will be available to the common users, thus opening the way to a huge potential of application and socio-economical developments.