From our recent developments of Project Sudoku, we've been able to change how we will handle our policy for the Legacy phones. In our original plan to bring our platform to 16.04, we were using systemd, which requires changes to a device's kernel to use versus Upstart. With Sudoku, we are continuing to use Upstart. This means that we can bring 16.04 to all of our currently supported devices.

We have begun creating 16.04 images for all supported devices. It is currently only for use by developers and testers and we welcome your contributions.
An excellent question. Going from 15.04 to 16.04 isn't easy, but it seems to be much easier than going from 15.04 to the (very early) 18.04. Similarly, rebuilding 15.04 sources on a 16.04 base isn't easy, but it is faster. Choosing the easier path means a faster release, which means we don't get left in the dust. Release early, release often.
In the OpenStore app running on Ubuntu Touch or browse online at the Ubuntu Touch Apps. The Ubuntu Store will be closing its doors at the end of 2017 and we will be working with developers to help migrate their apps over to the OpenStore.
All of the required packages for the system are found in our metapackage.

The packages we build are also in the repo.
Ubuntu Touch will now use the Ubuntu Installer instead of the MDT.

MDT tool can be found here.
Please join and get in touch with someone in our UBlangs Telegram group to find out more.
On any device running Ubuntu Touch you can check out the OpenStore app to see all the apps available in the official UBports store. To browse the collection from a desktop computer, please see uAppExplorer for a current list of available apps.