Less and less non-amd64-compatible i386 hardware is available for consumers to buy today from anything but computer part recycling centers. The last of these machines were manufactured over a decade ago, and support from an increasing number of upstream projects has ended.
Ubuntu and flavors just completed the 18.04 release cycle. This released version will either be supported until 2021 or 2023, depending on the product, team, and willingness to support it. At that point in time, the majority of these machines are approaching two decades old.
>>Previous 2016 thread: And in 2018, the question will come if we can effectively provide security support on i386.
We can't. Machines running i386 Ubuntu which are capable of running amd64 Ubuntu are vulnerable to the critical Meltdown vulnerability where they wouldn't be if they were running amd64. (Some actual i386 hardware simply isn't vulnerable, but some is).
We still have a relatively high number if i386 downloads but that doesn't mean users machines are not capable of amd64. For the flavors remaining today on i386 here are some i386 to amd64 ratios for 18.04:
Lubuntu cdimage - 0.87
Lubuntu tracker - 0.64
Lubuntu error (pcmanfm) - 0.11
Xubuntu cdimage - 0.49
Xubuntu tracker - 0.30
Xubuntu error (thunar) - 0.10
Kylin tracker - 0.30
Kylin error (engrampa) - 0.10
Kubuntu cdimage - 0.14
Kubuntu tracker - 0.12
Kubuntu error (kinit) - 0.07
The data retrieved from cdimage is for a limited time period on May 7th. All cdimage statistics included many hundreds to thousands of downloads (except Ubuntu Kylin due to it using it's own CDN, so not being included here). The torrent tracker results are available here: http://torrent.ubuntu.com:6969/.
The error tracker statistics come from comparing top bugs shared between i386 and amd64 over last week. Bugs that affect multiple flavors are not included.
It's not fully understood why there is a large discrepancy between the error tracker and other sources - but it's possible apport doesn't work as well in low memory.
With Ubuntu MATE, Ubuntu Budgie, and Ubuntu Studio joining Ubuntu Desktop and Server in not offering i386 support in order to focus their efforts, and these statistics in mind, we (flavors) should all join them. Now is the ideal time to do so, because it's before the Cosmic cycle is really under way, and if support were continued for i386, we don't want users to meet a dead end with respect to upgrade paths, and would support it until 20.04 (which means either five or seven more years of i386). Users still have the support cycle of 18.04 to use their machines and get full support, so these machines will still be able to function. But with no new machines being manufactured, we have to deprecate support at some point.
The first step would be to all agree on dropping images/installers but we should keep the end goal of dropping the port in mind ideally soon as well.
On the list of known blockers for removing the i386 port are Steam and Wine. Solus' snapped Steam is progressing nicely and Steam deb is difficult to maintain as is [See removal bug]. That leaves coming up with a good way forward for Wine.
[2016 email thread] https://lists.ubuntu.com/archives/ubuntu-devel/2016-June/039420.html (was Installation Media and supportability of i386 in 18.04 LTS Re: Ubuntu Desktop on i386)
[removal bug] https://pad.lv/1759715