The need for a major rebuild of the power network is overblown, at least at the 400V final distribution level. Re-conductoring is quite feasible with overhead lines.

Most often, what you will see is that when a new mid-size development (say, a dozen townhouses/apartments) goes in, it will include a new pad-mount TX/substation significantly oversized for that load. WE will run 2+ new underground 11kV to it (ring-main or mesh, to enable isolating a faulted cable without loss of load), new underground cable to the new load, and a few cables to the existing overhead distribution network, grabbing maybe a dozen customers from the nearest heavily loaded transformers. You'll frequently see poles where two 400V systems butt up against each other, but are not actually connected.

Fatter/more 11kV supplies are an ongoing project, but they are a bit more arterial. Same goes for the 33kV cabling, much of which is getting condition-based (i.e. end of life) replacement with a higher capacity anyway. There's a new zone sub (33kV > 11kV) or two going in over the next decade, and again, they just grab maybe a third of the load from the nearest three subs.