Most riders I know use a saddle bag for spare tubes and minitools, which will occupy a significant length of their seat post, which may already be quite short. Therefore fitting a saddle bag and a Varia Taillight onto the seat post seems to be a challenge for most and impossible for some riders.
I just spent a few days exploring ways to mount my new Varia RTL515 to a Topeak Aero Wedge saddle bag in size S and the suggestions range from clever hacks to overpriced pieces of 3D-printed plastics. Neither of them seem very satisfying. As a european customer I don't feel comfortable ordering an expensive 3D-printed plastic clip from the US with long delivery times, significant shipping costs and potential customs fees. Neither should a customer be expected to permanently bolt their light with custom DIY hacks to a potentially expensive saddle bag.
An officially sanctioned solution is needed here. This is not a question of price - an official solution might as well be expensive as long as it's reliable and widely available.