Webflow CMS looks great, it's hard to tell how for along this project is as the landing page shows something that is in early concept.
However the concept is great and I know your team has the knowledge to pull it off. I'm part of a small agency and I've used no end of CMS systems, from WordPress to Concrete5. However, this seems to tie in the design and development, cutting down potential work time by half (figuratively speaking).
However, I have seen systems similar to this before. I'm sure you will release more information further down the development timeline. However, I really can't let myself get excited by this until I know the following.
Is this self-hosted?
I think that's the most important for any professional CMS. Clients need it hosted on their platform.
What are the costings?
Is the CMS going to be free, maybe even open-source? If not, are we going to see a pay per site or an unlimited option? Hopefully we won't paying per page amount etc.
3rd Party Plugins?
Are you going to support 3rd party plugins? I think the biggest driver for WordPress is the plugins also we often develop our own depending on the clients needs. (such as mailchimp integration, e-commerce system).
If you say it's self hosted, open-source or £99.99 for an unlimited licence, with 3rd party support. Then we have a revolution.