Well, I have to say I am surprised by the lack of responses, I gues this new rpi is maybe not as popular as I thought it would be...mind you everywhere here in the U.K. sold out now... 
Sold out because it's that popular right now? 
Lack of responses (so far) is likely because the man working on it (@Wimpy, our project leader) just received the unit yesterday:
Like any development, porting can be easy, sometimes be tricky. It'll be some time before we get an ETA. Then again, it will only disappoint if the date is missed due to other factors. Other images got delayed in the past because of that.
But... we know it's extremely likely it's being worked on in the background. 
New to community -- G'Day all
I have a RPi4B desktop kit on order... I'd like to use the 64bit Mate rather than Raspbian !!
Love your work - thanks to all!
I'm a retired Software bloke (development, management, architecture etc. formerly with IBM software group and others over the years) from Aussie.
Hope to contribute once setup.
Regards, Kym
I won't be giving at ETA because I'll be working on this project in my spare time which will be in short supply in the coming months. I have 2 Pi 4 devices and am just as keen to get them running Ubuntu MATE as anyone else 
Totally understand and look forward to any developments....keep up the superb work...
This is an attempt to bring some realism, honesty and a 'can do' attitude to this thread.
Old images won't work with a pi 4 because they won't have the new bootloader firmware or Linux kernel. The Ubuntu packages that deal with these are Linux-firmware-raspi2, flash-kernel and Linux-raspi2. You can check for updates by looking them up on launchpad.net. Wimpy does not/never has maintained these packages. They are spin offs from Ubuntu core. For progress on Ubuntu core see this thread https://forum.snapcraft.io/t/support-for-raspberry-pi-4/11970 . Ubuntu core will also require a new version of u-boot for the pi4 (yet to be written).
Until these packages are in place there is nothing for Wimpy to do. And then it is just the trivial task of re-spinning the images.
For pi4 progress in the generic linux kernel check out this thread https://lists.fedoraproject.org/archives/list/[email protected]/thread/OFIGDPUDFOA3BB33GVCDHTSGZ2Q77APK/
If you want to run Ubuntu on the pi4 now then I suggest you copy the kernel and firmware from Raspbian. This is how ubuntu mate 16.04 used to work. If you don't know how to do this then look up the many threads on getting the 3B+ working.
Is anyone at Canonical working on this for Ubuntu Server or any other flavor? anyone knows of any update?
Seems to be some progress in Core - https://forum.snapcraft.io/t/support-for-raspberry-pi-4/11970/23 Hopefully this leads to progress on MATE release
While not an official installation, I have managed to bring Ubuntu-MATE 18.04 up on a Pi 4 as described in the thread "Is there Ubuntu MATE for the Pi 4".
I see that 18.04.2 Ubuntu Raspberry Pi 3 image download links are down everywhere. Does this mean we might be getting Pi 4 support soon?!?!?!? Let conspiracy theories start.
Maybe... maybe not.... the script that deploys the website was pointing at non-existent Beta 2 images... 
The downloads for the current versions has been fixed.
I have two of the Pi 4's w/4gb on order ...should be here in a week. (Aug 16th.) Was hoping the Ubuntu Mate for the 4 would coincide, but my review here indicates there is NO date set.
Your efforts are appreciated by many. Thank You.
Hi, I am very interested on the progress here. My Raspberry Pi 4 is ready and waiting for Ubuntu Server and/or Ubuntu Mate.
Keep up the good work.
@Hal58 has written a guide on how to get the existing Ubuntu MATE 18.04 running on a Raspberry Pi 4, using Raspbian and a Raspberry Pi 3:
It's worth having a look in the meantime until a new image is produced.
Was super excited to get my raspberry pi 4!
The Rpi3 B+ was just not fast enough to make a server, but the Rpi4 is. Torrents, DVR for IP cameras, and video player (it should be better at 4k than my Nvidia Shield TV is).
Got the pi4 in, installed Raspbian, plugged in my 8TB external drive and of course, ERROR. Won't recognize file system. Checked for solutions, seems like not many people have the rpi4 yet so I couldn't figure it out. Tried multiple external drives, none of them work! No worries, I'll just install Ubuntu!
That got me here. Will have to wait! Excited for the first release!
What file system is on your hard drive?
Ntfs. Nothing fancy. I have not tried a freshly formatted drive. I cant.. I don't have an extra 8tb lying around to copy it over if it works.
All the drives work fine in windows.
The second post I made in that thread describes how to get a Pi4 up with MATE 18.04 via an upgrade from 16.04 and actually results in a more stable system. I have done it several times and just put a 4 GB Pi 4 in service as a workstation with an SSD in a USB3 enclosure with a clone of the 'PI_ROOT' partition on the SSD. Over 300 MB/s reported by hdparm and it is FAST!
The first procedure I documented has a glitch in that the system won't show the login prompt until I press CTRL-ALT-F1 (or F2, 3, etc) and then just wait and the login prompt will appear. Another problem that seems to appear in all installations is that is you don't see the powerup script try using the other HDMI connector. I have had different installations using alternate video ports.