Layman users shouldn't notice any change, by design. It's an init system, not something users traditionally interact with. It should completely replace the functionality provided by Upstart —and do a few extra things— but the only time a non-technical user will see this is when it goes wrong.
Users, sysadmins and developers who have been actively using and developing for Upstart are the people who need to address things. There is a migration document on the Ubuntu Wiki to help developers convert their init scripts, but users and sysops can carry on using Upstart by sticking with 14.04 (which is supported until 2019).
The reason and rationale for change really wasn't from Ubuntu's side. Canonical were happy enough with Upstart (their project) but many Debian users wanted to move to a modern init engine to get better concurrency at boot and better monitoring functionality across all services.
That meant a fight between various options (the rationales) and systemd eventually won.
Canonical went along with Debian because it's easiest and probably best. They get to drop a project and aren't fighting upstream. It also brings us in line with other distributions (Red Hat, Fedora, etc) who are also moving to systemd. More focus and less duplication of effort.
tl;dr To a non technical person, this shouldn't affect you at all. For Ubuntu it should mean less work and a better init system.
Best Answer
Unlikely anyone will be able to answer this based on facts but I would assume that ...
switching from GRUB like you can do now (at run time) is likely to disappear and this is also likely to happen when 16.04 LTS arrives. During the Ubuntu Developer Summit (UDS 14.03) Mark Shuttleworth announced that systemd will be used as default on the next LTS version of Ubuntu, Ubuntu 16.04.
but as long as the package is available you can install it yourself. 15.10 still has upstart. How well new services will be supported by upstart is anyone's guess. Even I myself doubt it will be supported.
So I assume the answer is yes but with increasingly difficulty. I would forget about upstart and get to know systemd. In this case I would advice to not swim against the current.