Right now, the Sony sensors are (roughly) at technological parity from APS-C on up to 54x40mm MF - all are modern, copper-wired BSI designs, and all perform very similarly per pixel. Several of them (26 MP APS-C, 100 MP 33x44mm, 150 MP 54x40mm) actually seem to be the same pixels in different sensor sizes). There are three blips in this trend...
1.) The 50MP 33x44mm sensor is NOT of this lineage - it's a full generation or more older (non-copper, non BSI), and it barely competes with the 40+ MP modern 24x36mm sensors despite its size advantage. The 100MP 33x44mm sensor is the representative of the modern Sony lineage, but we only see it on the market in one industrial camera (the GFX 100 will be the first "standard" camera to use it).
2.) The 40+MP 24x36mm sensors are of roughly the same technological generation, but they are not the same pixels - the pixels are a bit bigger (just over 4 micron, while the others are all 3.76). Sony datasheets have shown a 61MP 24x36mm sensor, which will use the "standard pixel", but it hasn't cropped up (sorry) in any camera yet.
3.) If the 20MP Micro 4/3 sensor is a Sony sensor, it is a much older generation, technologically closer to the 50MP 33x44 sensor, and it uses a smaller, nonstandard pixel size. A "standard pixel" Micro 4/3 sensor would be around 15MP.
Once we see those two sensors (100MP 33x44 is probably a significant improvement, 61MP 24x36 is probably incremental because the 40+MP generation is already modern), there will be a wide range of cameras with very similar per-pixel behavior - it's just a matter of how many pixels you want to carry and pay for.
Essentially all non Sony-derived (counting both XTrans and Nikon/Sony designs as Sony-derived) sensors underperform the Sonys. The initial Photons to Photos results for the Leica Q2 sensor (probably TowerJazz, and probably also the Panasonic S1R sensor) show that it behaves much more like a high-resolution Canon sensor than a modern Sony. The default assumption about the Canon 70ish MP sensor is that it'll probably perform like a Canon, but maybe they've made a breakthrough.
Beating the Sonys may well take a new technology, whether it is organic sensors, a Foveon with the bugs out, or something else.