Maxwell will scale from 200W+ discrete graphics cards down to 2W to 3W SoC Tegra parts and should offer much better performance per watt compared to Kepler generation. The first card codenamed GM107 is coming as a desktop part and mobile parts are shortly behind. Mobile versions will be ready for Intel's Broadwell notebook refresh that should happen in the second half of 2014.
Tegra based on Maxwell comes in 2015 and should offer significant performance boost compared to Tegra K1 SoC parts. Maxwell will also be Nvidia's first GPU to be licensed to various SoC makers. The cost of GPU IP in mobile SoCs is relatively low, but licensing might help Nvidia gain more market share and reap the benefits down the road.
Gaming on phones and tablets is destined to become a lot better and mature, but still games on tablets are years behind next generation console or mainstream PC gaming. Battlefield 4 and Titanfall as well as Call of Duty and similar games will continue to look their best on PCs and next-gen consoles, but older titles will find their way to future tablets and make the gaming on tablets and phones a bit better.
It is like reliving the high-end graphics market ten years ago - what was high end for desktops ten years ago is coming to mobile phones and tablets today.