I would like to contribute a patch for this, but I have a few questions before I can do that.

Now PHP 7 is out, fatal errors no longer need to halt test execution. It looks like appropriate place in makeCall method in in the CallCenter class

public function makeCall(Call $call)
{
    try {
        $filteredCall = $this->filterCall($call);
        $result = $this->handleCall($filteredCall);
        $filteredResult = $this->filterResult($result);
    } catch (Exception $e) {
        return new CallResult($call, null, $e, null);
    } catch (\Throwable $e) {
        // Cast \Throwable to \Exception?
        $e = throwableToException($e);
        return new CallResult($call, null, $e, null);
    }

    return $filteredResult;
}

I have something along these lines working however I am not sure how to handle the cast of Throwable to Exception in the context of Behat. Symfony handles it via FatalThrowableException but to be frank I don't fully understand the constructor of that class, why is ErrorException instantiated but not assigned for example?

I would appreciate any pointers to getting a PR open (or a PR would be great too)