Canon does not have a new sensor ready. The only reason for delaying 70D is to add enough features to compete with D7100, at 20% less resolution. The ISO performance has to be 4 times better than the competition at $1000 level. If they had released 70D without these possible improvements, it would have been DOA (especially after D7100).
The 70D will have improvements in body (still metal+plastic), swivel touchscreen, under 6 fps, Wi-Fi and GPS but better AF and video. It will have new 360-degree dial, creative filters, etc. It won't be priced over $1150 (if it has to compete).
The biggest features on 70D will be the latest DIGIC processor, improved software and AF system. All other semi-pro features will be for 7D m2, including dual processors and new sensor.
They could do a new sensor with more than current 18MP but it won't be much higher than 20MP.
Canon is promoting 60D and T3i around the globe with heavy discounts. 7D in comparison has lighter discounts. The discounts on 6D ended. That shows what they want to get rid of and stop producing soon.