30fps is sufficient for reading plates, 60fps does not improve plate readability. If you have 2x the number of frames then you need 2x the bitrate to get the same quality, normally it is better to use the extra bitrate on improving the 30fps image quality than to use it on 60fps. There are a few exceptions, such as for use on race tracks where people are driving 2x faster than normal.
The real benefit of 60fps is that you get smoother videos, they are much better to watch, especially for dashcam video where we use very fast exposure times to avoid motion blur on plates, so it will be very nice to have a dashcam that can give good quality 60fps front video. I'm not sure 60fps rear video is needed though, people rarely make road movies using rear camera footage, and if someone wants to do it professionally then they could use two A229 Pro for front and back.
I am expecting a 2 channel A229 Pro price to be less than a 3 channel A139 Pro. It does have a newer and more powerful processor, with a few new features, so it would be reasonable for it to be more than a 2 channel A139 Pro, but maybe the 2 channel A139 Pro price will drop and the A229 Pro will take the current 2 channel A139 price.
Pity it doesn't have the IMX 585 image sensor in the graph above, that has single frame HDR