I mean they should have developed a new sensor.
Olympus does not develop any sensors that I know of. They could have selected a different sensor from a third party, with higher pixel density, but I do not believe that any sensor currently available on the market can deliver a higher resolution while at the same time equal/higher Signal/Noise ratio AND equal/higher DR, hence there would be a performance cost to using a higher density sensor at the expense of Noise and/or DR and the overall performance would drop below that currently offered on APS-C 24Mpix (which is marginally superior still to the best 16Mpix M43 sensor available right now).
Photosites on 16Mpix M43 sensor are 1.08x smaller than those of a 24Mpix APS-C sensor, and would be 1.63x smaller if it were 24Mpix M43 sensor, how can M43 possibly compete on Noise and DR with such smaller photosites? Hence, noise control is perhaps the most challenging issue with M43 at the moment. Recent developments on NR algorithms have closed the gap, but nonetheless, the sensor technology still has to come a long way and the RAW noise data hasn't changed all that much in the past two years.
Don't you think that Olympus wouldn't jump on it if it was such a sensor available? This is what every camera manufacturer dream of.