As suggested by the name and explained a bit by the issue, some Delta Chat devs want to add .tgs format, based on Lottie, as option (and could be main format by now) for stickers pack and this is where they are starting.
The format was added recently in a Delta Chat fork called DeltaLab (https://github.com/adbenitez/deltachat-android).
I had a little private discussion with the author about his proposition to influence Delta Chat devs for using it.
Lottie has a closed specification as far I saw but some libre tools are provided by default to support it. The format is also not-standard and not implemented over everything.
I proposed SVG/SVGz as an alternative, given some work made in https://gitlab.com/mattia.basaglia/python-lottie/ but animations on SVG/SVGz as output are not finished, in private discussion with the DeltaLab's author but after denying SVG without checking possibility of what he wanted for cubans, small size stickers comparable to Lottie, he didn't reply to that proposition.
I write this post because I am worried about the situation on Delta Chat. It is not that I want .tgs and Lottie compatibility to be denied, is that I want to ensure that this will be in order to add other capability over a fully standard compliance sticker implementation, with low size given what SVG is and SVGz, that could finish in a conversion from .tgs.