The issue with poppet valve 2-strokes is achieving good scavenging efficiency. With a conventional diesel combustion chamber; 4 inward-opening valves with central vertical injector, it is difficult if not impossible to direct the intake flow to loop down the cylinder on one side, and then back up the other side and out of the exhaust; it has every incentive to short-circuit straight out the exhaust.
To get reasonable scavenge efficiency, you have to go with downdraft ports on the inlet side (which is what Ricardo did for their "Flagship" SI poppet-valve 2-stroke), but this is formidable to package around the injector.
You can argue that today when all engines use EGR (and usually lots of it) that good scavenging is not so important, but hot residuals are only ~50% as effective as cooled EGR at NOx mitigation, so you really want cooled EGR even in a 2-stroke where the combustion temperatures are lower (than in a 4-stroke) anyway. Plus, you still need to get the fresh air for the next cycle in on top of the residuals, and there is not much time between EVC and IVC.
So, with a 2-stroke diesel, you need to have directed intake flow for good scavenging efficiency, but you will still likely need well-controlled swirl to get good combustion efficiency. Achieving both requirements is not easy with a conventional chamber.
PJGD