Seeing the conflicting opinions here, I want to clarify something ...
The diffences between 5.4, 5.5 and 5.6 aren't as impactful as they were with PHP 5.2 vs 5.3, where namespaces were a total game-changer. The version tree (5.x) might be the same, but while these are all minor versions, PHP 5.3 is really to be regarded as a major one. This is mostly due to the cancellation of PHP6 - a lot of code and features that were supposed to be in version 6 went into 5.3 instead.
In addition, having a minimum required version does not necessarily mean to use
all of its capabilities, just as with supporting newer versions. It simply means that it
will be guaranteed to run on that version - nothing less, nothing more.
That being said, I believe you're over-thinking the issue here. IMO, the discussion should be focused on what PHP version you'd
expect to run your CI4 code and how reasonable these expectations would be, both in terms of PHP version adoption rates and security/common sense considerations.
For example - I can certainly do just fine without PHP 5.5's generators, but I also realize that 5.4 will be EOL'd before CI4 is released. At the same time, I'd love all of PHP7's new capabilities, but let's be honest - it's not even in Beta stage yet. So, I'd look for the balance in between ...
Note: This is my personal opinion and NOT an official statement in any capacity.
