I would like to have something like an LED bar, except that the light emission should not be broken up into separate lights, but be more or less continuous - without much greater light intensity per length.
Finally, it should be used for a thin, flexible rod of 2 m by 3 mm like the one described in Light LED light?, so it needs to be somewhat flexible, and not very bulky. I think that short sections of inflexible sections would do.
One way to do it would be just using a continuous row of adjacent SMD LEDs, and using a very low current to reduce the emission per length.
It would need to be assembled from a a lot of LEDs.
Also, there is the problem that differences in individual LEDs are much more visible at low current, so it may be that binning LEDs is needed.
There is something very similar to what I need: Filament LED bulbs, which have LEDs imitating carbon filaments in an old bulb.
These filaments are actually COB LEDs, where the board is a thin inflexible rod, covered with the LED material in some way - maybe tiled separate dies, covered again with the resin.
The filaments are just right, except that they are too brittle to be bent, and too short.
In the product description of a filament bulb, you can find pictures of filaments: