ClearOS provides its own DDNS client and naming, but it does not allows for the configuration of any other DDNS services through the web interface. Its possible to setup other clients on the system but only by command line and not integrated in the web interface.
Ideally the system should provide a way to configure the most common DDNS providers through the interface. This is required because in many cases there is an existing DDNS name being used already and it can not be disabled or replaced easily as other systems and people my be using it.
At least these Service provided should be added:
There is a program called ddclient which can do this. It can run in daemon mode or fired off on demand. If you wanted to fire it off on demand, you could hook onto the ClearOS DDNS mechanism for detecting a new IP.
It supports a lot of DDNS providers with pre-written configs just waiting to be uncommented.
It has different built in IP detection methods which can work if ClearOS is directly connected or if it has a LAN IP (so is sitting behind an unbridged modem/router)
Some DDNS providers require you to revalidate periodically - every 25-30 days. In daemon mode ddclient can handle this.
As an alternative, OpenDNS has a sister site DNS-O-Matic which it uses to keep track of your IP address if you have an account with OpenDNS and have enabled the DDNS option. DNS-O-Matic can not only update OpenDNS with your IP, but it can also update a huge range of other DDNS providers. In this case, all you'd need to do is create a program/routine to update DNS-O-Matic and let the user configure DNS-O-Matic to do the rest. Ddclient supports DNS-O-Matic (I use it), but it may be overkill to use it for this if you are programming your own front end.
Multi-WAN is a possible complication. ddclient can handle it if the WAN interfaces get the public IP. I am not so sure in the case that ClearOS is behind NAT.