Well, i tried already to post, but that post did not appear..., here my second try:
Hi, i'm very excited about this, because we use Ubuntu at our company. I have many suggestions, perhaps i can describe them better this second time :)
MultiMonitorSupport and HDPI were already called for, so i will not repeat that.
I'm very well aware that you cannot and won't do most of this stuff, but any of this done would tremendously help you and all ubuntu users. And do not think i think Ubuntu is not great. It is. But there's always room for improvement. You guys are the best for asking here!

I am a developer and kind of architect at our company. and we have a downstream distribution of ubuntu. we try to upstream our stuff, but that's not easy with our resources

- FLAVOR: Ubuntu Desktop, Ubuntu Server, Ubuntu Core
- HEADLINE: support reproducible builds
- DESCRIPTION: reproducible builds will help us to write better software and verify software on systems bit for bit, this is an tremendous effort, which will possibly help us all with software quality

- FLAVOR: Ubuntu Desktop, Ubuntu Server, Ubuntu Core
- HEADLINE: provide fuzzy build recipes
- DESCRIPTION: provide fuzzy build recipes (with afl-fuzz for example) with each source package like for example https://github.com/d33tah/afl-sid-repo so it is possible that we can test the software and find bugs. you won't find all the bugs because you cannot test for all inputs, but if you provide the recipes most will try that on their own systems with the input which is important for them

- FLAVOR: Ubuntu Desktop
- HEADLINE: please provide more apparmor profiles
- DESCRIPTION: the desktop is a interesting attack surface, please provide more apparmor support for example thunderbird, okular, libreoffice, calligra flow, calibre, gwenview, gimp, kate, xpdf, since email, pdf, images and office documents are common attack vectors. perhaps even provide multiple versions for more or less strict version for example for firefox.

- FLAVOR: Ubuntu Desktop, Ubuntu Core
- HEADLINE: make poppler/okular better!
- DESCRIPTION: poppler is an important kind of piece, many depend on it. but i miss important functionalities like layers (https://bugs.freedesktop.org/show_bug.cgi?id=97768) or xfa-support which is needed for government papers to fill out :(

- FLAVOR: Ubuntu Desktop
- HEADLINE: better citrix support
- DESCRIPTION: citrix web receiver and the ica client are not nice to use. Perhaps you could collaborate with them and make it nicer. Responsivness, speed and image quality often lacks on ubuntu/linux machines :(

- FLAVOR: Ubuntu Desktop, Ubuntu Server, Ubuntu Core
- HEADLINE: make a citrix alternative?
- DESCRIPTION: or instead of citrix you could build a alternative to citrix with libvirt/kvm and spice? :D

- FLAVOR: Ubuntu Desktop
- HEADLINE: Support kube
- DESCRIPTION: Kube (kube.kde.org) is a new emailclient based on qt/qml, written by kolab and could be a replacement for thunderbird, which is barely maintained. and finding people who can hack on thunderbird/xul is not easy.

- FLAVOR: Ubuntu Desktop
- HEADLINE: integrate usbguard for enterprise
- DESCRIPTION: usbguard is a tool for white/blacklisting usb-devices. please integrate it and make a version, where it can use signed data from other remote sources! :)

- FLAVOR: Ubuntu Desktop
- HEADLINE: integrate clevis/tang
- DESCRIPTION: clevis and tang would support device encryption and make a second decryption key which is important in enterprise settings, WITHOUT pressing the user to reveal his own key.

- FLAVOR: Ubuntu Desktop
- HEADLINE: better beamer support?
- DESCRIPTION: when i put my ubuntu box to a dvi/hdmi beamer i often see the display only after rebooting. could you make it work that it works already after plugging the beamer in? with other distributions like fedora it often works :(

- FLAVOR: Ubuntu Desktop, Ubuntu Server, Ubuntu Core
- HEADLINE: more security support
- DESCRIPTION: either put more packages from universe/multiverse to main or support security updates for packages in multi/universe too. This is not easy for users to know, what is insecure on their box. or at least make it visible via a commandline tool?

- FLAVOR: Ubuntu Desktop
- HEADLINE: docx support?
- DESCRIPTION: make libreoffice with docx support better... yeah, it is not a nice job to do :(

- FLAVOR: Ubuntu Desktop, Ubuntu Server
- HEADLINE: enable kernel live patching and activate it with unattended-upgrade
- DESCRIPTION: enable live kernel patching and enable unattended-upgrade for it that it supports ith with configuration.

- FLAVOR: Ubuntu Desktop
- HEADLINE: make joining ad/ldap+kerberos environments easy
- DESCRIPTION: make a tool, that makes joining an AD-environment or kerberos/ldap-environment really easy. bonus if you provide such a server environment via configuration/debpackages yourself!

- FLAVOR: Ubuntu Desktop
- HEADLINE: NetworkManager and secure certificate support
- DESCRIPTION: In Enterprise Environments it is often needed to have Certificates for 802.1x, openvpn or openconnect. It would be great if networkmanager would support pkcs-urls (and the tools which are used by networkmanager) which then connect to a softhsm and the certificates are only available for the networkmanager, which is enforced via apparmor-profiles

- FLAVOR: Ubuntu Desktop
- HEADLINE: security audit of qt
- DESCRIPTION: Martin graesslin mentioned in a blog post that qt is not vetted for security, it would be great if there's a security audit for it

- FLAVOR: Ubuntu Desktop
- HEADLINE: make a function/syscall for erasing memory secure in qt
- DESCRIPTION: Enable a possibility with QT (perhaps even with a syscall) which erases memory secure even within the qt-environment?