I like the simplicity of the login/greetings page, but it would be nice to have some more customisation on our hands:
Various other login options (PIN, via: Social media (FB, Google, Apple, Twitter(X))), voucher, MS Active Directory, …, a custom field, where guest would fill in required fields (Name, Surname, …), and For free button).
Background colours and images
Fonts and font colours
A preview button for mobile/desktop view
ADs (a video can be played (and not skipped) for set duration of time)
Some ideas/request that our customers have (Hotels, Education, and Corporations)
At this time, I think you could integrate an external portal to implement most of those custom features. Perhaps all of them, in fact. Could that satisfy your needs until we have an opportunity to develop the local portal more?
I am not familiar with vendors of guest portals at this time. Many people integrate their own, and you can get started by pulling down the advanced settings on your SSID and enabling the Hotspot.