Can someone please explain why this question of mine was closed as "too broad". It seems to conform to the site guidelines. And it is very specific.
I probably wouldn't have voted to close it but it feels overly broad to me in the sense that there are a lot of distros that will fall into this category, and that list will change overtime, so there won't be a consistent answer to your question.
The other bit, and you do say "default" so you're trying to restrict the question's broadness, is that who's to say that a 3rd party repo that's well supported, isn't in play when discussing what one would consider as "default".
For example, I'd consider the EPEL repo as "technically" part of the default, even though you have to add it, given it's well maintained and pretty core to most anything you'll want to do on a CentOS distro.
Other distros will vary, but I suspect there are repos similar to this in other distros as well.
Again this is just my $0.02 on this but this question just has a air of broadness that it cuts just too close to the edge, IMO.
There are either too many possible answers, or good answers would be too long for this format. Please add details to narrow the answer set or to isolate an issue that can be answered in a few paragraphs.
At time T1, $RANDOM_DISTRO1 plans to add PHP7 as a default. It's an answer.
At time T2, $RANDOM_DISTRO2 plans to add PHP7 as a default. It's an answer.
At time T3, $RANDOM_DISTRO3 plans to add PHP7 as a default. It's an answer.
At some point, most distros will have PHP7 as a default. The question is meaningless.