I used to work at an OEM, we were looking at retrofitting with LED 15 yrs ago including for GA airframes, but couldn’t justify expense at that time. The financial reward for certification activity simply wasn’t there for the manufacturers to do retrofit.
LED approvals need to go through an ELOS - equivalent level of safety certification process to demonstrate compliance, which is why adoption has taken so long.
As you know PZL, an airline often has its own field engineering group to design and disposition field repairs & out of cycle maintenance. US airlines have been able to successfully use their in house engineering to approve LED retrofit for their fleets. It makes more sense for airlines because they’re buying these bulbs in bulk and getting burnouts and spending maintenence hours on remove and replace whereas the LED has better durability and reduced power requirements.
As a result, they are being converted in the US presently. When you look up here, you are now just as likely to see LED lights including nav, flashing beacon, landing lights and high intensity anticollisions, regardless of year/manufacturer/airframe.
On addl side note - on this side of the world, it is common practice to leave nav lights on at all times, including at the gate, regardless of whether plane is LED equipped or not. Usually we shut down all power including nav only when down for the night.
Ice inspection