What ever happened to consistent, cross-application look-and-feel? I don't want each application defining its own style which clashes with every other application. We already have things like Qt and GTK themes for the desktop, but the web is just a mess in that regard. I really hope to see some eventual solution.

Mozilla's "Reader View" is a fantastic step towards establishing a consistent (and user-configurable) look-and-feel across the web. But its domain is still very narrow and wouldn't apply to Slack, unfortunately. Yet it's the only product I know of that's even working towards this kind of goal.