Kirby should provide an ‘official’ root for logs.
Many plugins log stuff and it would be nice to have a dedicated directory for that, even if Kirby itself doesn’t write any data there. When used inside a plugin, a Logger class/utility (maybe like @bvdputte‘s kirbylog?) could write to a folder named after the plugin.
Some plugins place their logs inside site anyway - so if I configured it to be somewhere else, all plugins using this core feature would follow this decision rather than writing to a hardcoded destination.