@bloodchen the core team is mainly focused on developing one standard basic theme that hopefully is easy to modify yourself. We've been pumping out tons of custom themes for our enterprise clients, at least half a dozen per year on average (I mean, we also have to eat.). We have a small team that works on theming (see what I did there), so naturally that is the state of freely available open source themes at the moment.
Anyway, the next theme will be based on react and/or vue (your choice) and I hope that we will be having more open source themers in the future.
Thanks for the feedback.