Questions regarding Webp format / Maintenance mode

Hi,

I am planning to use Webp format to optimize my homepage load time. I would like to get all my pictures automatically converted before they are displayed. 
Is it an option you are planning to implement?

Is there a maintenance mode that can be activated? I am thinking of a single page replacing all website pages. This page would load as long as the maintenance mode remains activated. Would be really useful!

Thank you

Best regards,
Eric