This doesn’t sound practical to me.
(1) Carbon build up will eventually cause pre-det issues with the natural gas being sucked in through the intake stroke, as the engine ages.
(2) Have to put two fuels in your car, granted it won’t be a lot of diesel all told, still annoying.
More practical would be if they had figured out a reliable injector pump design that could inject CNG into the cylinders at the required pressures for diesel ignition of natural gas. That is probably a very tough problem though... mechanically speaking. Also, increasing engine robustness while reducing weight, to handle the higher compression ratios required (ethanol takes 23:1, I’d expect natural gas to be somewhere between ethanol and diesel... have not looked this up).
We have "dual fuel" trucks in the US, that run on natural gas or diesel. While there's natural gas, it runs with gas plus a little diesel. When the natural gas tank is empty, it runs on pure diesel. This is a more practical arrangement until the natural gas infrastructure is built up better.