ocramius, Looked again at a #PHP codebase written/maintained in PHP 5.5, where new code is designed and added on the existing app.
Made me realize that the only thing I miss from newer PHP versions is strict type checks, which came with PHP 7.0.
Everything else was provided by @psalm or @phpstan
From my PoV (person that reads internals, follows/votes on RFCs, etc.), there are almost zero feature additions that make newer PHP versions interesting.
Not justifying staying back: just noticed this.