The increases pixel density and faster chips would make APS-C DSLR bodies in the future obsolete. But ... as long as APS-C costs significantly less ($655 for the 60D today on Amazon vs. $2,000 for the 6D), the crop format would keep being a good way to lure enthusiasts into their dSLR system.
Increases in pixel density means increases in file sizes. 33 MB for a RAW file from a 5D III is enough for me, thank you. The APS-C crop requires only 40% of the file size.
5D IV, 5DS R, 7D II, EOS-M, Powershot G3 X, 400mm DO II, 300/2.8 II, 1.4xTC III, 2xTC III, EF 1.8 STM, EF 70-200/4 IS, EF 24-105, 15-85, 100-400 II, Sigma 10-20, Sigma 150-600mm C, EOS-M 18-55, f/2 22, 11-22