Cloudmin needs to support IPv6 soon IMHO as its something that providers should be getting reading for and/or already be using.
It also needs the support for multiple network interfaces. For example:
1) One WAN interface 2) One LAN interface 3) Private VLAN between clients own instances.

Multiple interfaces
Support for multiple interfaces is definately planned, and should be available in a release or two.
IPv6 support may take longer .. although I guess with Xen guests could bring up their own IPv6 addresses already anyway.
Hi Jamie, Has the option to
Hi Jamie,
Has the option to add multiple interfaces been introduced yet? I can't seem to find it.
multiple interfaces
Yes, if a xen host has multiple bridges setup, and you select them on the Edit Zen Host page, you can gave multiple interfaces for your xen guests.
Hi Jamie, Sorry, I might
Hi Jamie,
Sorry, I might have used the wrong words. How do I assign more than one interface (and ultimately) IP addresses at creation time? i.e. when I use "Create System" > "Create Xen instance". How can I assign more than one IP at this stage?
Multiple IPs
If the host system you select has multiple bridges setup (on the Edit Xen Host page), you will see fields on the Create System page for entering multiple IPs. These will then be assigned to eth0, eth1, etc.. on the Xen guest.
Hi Jamie, Is it not possible
Hi Jamie,
Is it not possible to have the IP's from the same range on one interface, as aliases? i.e. eth:0, eth0:1, etc.
The reason I want to suggest this, if it's a suggestion, is that we have some VPS client with sometimes upto 40 IP's per VPs.
And I would rather use the eth1 interface for locate networks (i.e. SAN backups), and keep eth0, eth0:{0-40} for public usage. Is this possible, or should I put in a feature request for it?
Multiple virtual IPs
Sure, that is possible .. on the system creation form, you are only setting up primary (non virtual) IPs for interfaces like eth0, eth1 and so on. After creation, you can add more virtual IPs on the System Configuration -> Network Interfaces page.