Linear drivers will stay in flashlight world as long as source of light are LEDs, they are smaller, cheaper and have higher power density compared to switching drivers and that will not change. Also linear drivers can have wider dynamic range of currents without large penalty in efficiency,for ex. it's much less challenging to make linear driver with output adjustable from 0.1mA to 20Amps.
Another advantage is driver quiescent current while driver is active - it can be in xx uA range, which is almost impossible for switching drivers (mA range), so runtime on moonlight/very low modes can be significantly better with linear drivers.
While switching drivers in theory have higher efficiency, in practice (single cell - 3V LED) difference in average efficiency is 5-10% typically - not as high as many here claim. Reason for that is battery voltage drop, so linear drivers maybe start with ~75% efficiency when battery is full, but as battery voltage drops efficiency raises to ~100%, so average efficiency is somewhere in between, depending on which mode you use the most. If flashlight is mostly used in lowest and highest mode, there is almost no difference in efficiency because switching drivers efficiency is not that high either on those modes.
Switching drivers are only option when number of cells in series is not equal to number of LED "dies" in series.
