I'm not an electrotechnical engineer, but I'm not sure that converting the (existing) power distribution grid to DC could be a wise operation, not even a cost effective one.
Transformers in the grid are very efficient devices and have the bad habit of lasting lots of years. Should we send them to recycle (a dumpster somewhere in Africa or Asia) and spend money for new equipment? Somebody will be happy: the converter manufacturer--
The converters (from hi voltage lines to mid and low voltage lines) will be electronic, with the associated reliability issues.
It's the same with wall warts: the old ones, with laminated core, 50 Hz transformers, if correctly and not too cheaply designed, will outlast all the new switching units. I have examples of standard low-power supplies (one is powering my condo's door bell system) that are operating, 24/24, from the 80's.
Best regards