@thesergie I can't speak for everybody here but I think what he was referring to is having something on each individual site's backend (in the hosting or billing section) where you can email an invoice to your client for the amount of $5/basic hosting or $10/CMS hosting. I'm not sure everyone utilizes the "Organizations" feature as often as one should and so they add the clients site to their own personal webflow account, but would like to bill them separately for the hosting.
If this does happen in the future, I would like to see our personal branding (logo or colors etc.) in the invoice that get's sent out, which can still incorporate webflows logo as well. It makes it more professional and easier to trust us when we send a form for payment through email.
As far as actually billing clients a monthly fee for web design services, I guess it all depends. We handle branding, visuals, advertising (billboards, posters etc.) so it's a lot more than what the average person would charge for web design and development. Although I know a few different people who would benefit from this, maybe @DanUK1 or @buntestrahlen could weigh in on this more and help with a better answer.