There are three main issues that led to this decision:
- All computers with Windows 8 pre-installed come with UEFI, and therefore have GPT disks which grub4dos does not support. And Wubi requires grub4dos in it's current form, so it doesn't work.
- The 13.04 disk-images (pre-installed Ubuntu images) that Wubi uses were broken for some unknown reason.
- Even without the disk-images it is possible to use an Ubuntu ISO to install Wubi, however, another bug prevented the 64-bit version of Ubuntu working with Wubi.
Based on IRC logs, these three issues were discussed during a release meeting and it was quickly decided that it wasn't worth it to put in the effort. This decision was then taken to Canonical and apparently no-one there had any objections. It was then posted to the Ubuntu Devel mailing list and, again, no objections.
Is Wubi really gone?
So, decision made. However, apparently the 12.04.2 Wubi.exe will still be available, as will the 12.10 Wubi.exe, which means there is support until at least Apr 2014 (for 12.10) and Apr 2017 (for 12.04). It's also possible to upgrade from a previous install - so anyone who really wants Wubi can get it without too much hassle. And a case in point is when Xubuntu was pulled from Wubi 12.10, my blog post on how to trick Wubi into installing Xubuntu became the most popular on this site.
It should be straightforward to generate a working Wubi for 13.04, notwithstanding the 3 issues shown above. Problem 2 and 3 are basically solvable with a single configuration file change. No, it won't solve the UEFI issue (problem 1), but - the truth is, even installing a normal dual boot with UEFI is not exactly problem free: the current community recommendation for installing it is to use an unofficial boot-repair tool to make up for the myriad of bugs associated with this "improvement to BIOS". And since there are still many people with computers that don't support UEFI, Wubi will still work.
How popular has Wubi been?
I'm really curious on the actual stats on Wubi use. It's clear it's been popular amongst newcomers to Ubuntu, but it'd be interesting to see the actual stats and weigh that against the quick decision to pull it. Either way, it's clear that it has helped bring many people to Ubuntu.
**Update April 25 - Release date**
With the release of Ubuntu 13.04, no change was made to the decision to discontinue support, despite a patch being provided by me for all three bugs. However, a signed, patched (all except the UEFI issue) version of wubi.exe is currently available at http://releases.ubuntu.com/13.04 so it's unclear what's up.