I am planning to mainly work on the performance and shrinking the databases. Some changes may require special patches for mapnik, but I'll submit them upstream. For example, I think I found the way to reduce maps significantly, about to the half of their current form. To my surprise it did not effect the performance (initial testing on onyx), so we should probably switch to that. However, that means I would need to keep two versions for the style - one for mobile with all patches applied and the second for PC and style design.

For best performance, I tune the database layout to match the style. This means that if we want to make major changes in loading sequence, we would be better off to tune the database too. Which is not a major issue, as long as we remember it. In particular, you would want SQL SELECT statements in https://github.com/rinigus/osm-brigh...spatialite.mml to match SQL database as arranged at https://github.com/rinigus/osm-brigh...reorganize.sql .

I have not looked into GUIs on style editing. Someone who wants to adjust styles, should probably look into https://github.com/kosmtik/kosmtik or https://tilemill-project.github.io/tilemill/ . TileMill seems to come in a package that installs mapnik as well. So, its not good for me (I have to use a custom one), but could be great for a designer. I don't know if they come with SQLite plugin enabled though. kosmtik I tried, but it didn't seem to work on my Linux PC immediately, probably some tinkering is required.

Anyway, to contribute to style development: we could collect the ideas either here or in issues of the style project; try to setup GUI and see if it works. I'll be happy to help if you run into problems with the setup of GUI, as much as I understand how it works.

If there is someone interested in working on a style, let us know and see how we can help.