Are there any news about that?
I have the same situation in our company. We have about 200 Tablets in the Meraki MDM and in Kiosk mode.
Overall im really happy with Meraki, but not with the design from the Kiosk mode. The worst thing is that you can not even change the logo. It's really sad in a company like Cisco... Because on the other hand, in the Meraki Wifi settings for the Splash Site, you can change the logo, the color, etc.
I really hope that this feature will come in the near future as an update. We would need this.