Wi-Fi was almost certainly more difficult to install on older stock, just as I expect PIS and CCTV systems were, but all new trains would be wired to make it easy to add-in later (but any sensible operator or ROSCO would probably install the whole Wi-Fi kit at the time of production, which they realised part way through the 700 build).
As zwk500 says, the cost is negligible in the grand scheme of things - especially as modern trains will have network connectivity for its own systems and diagnostics. The amount of kit on a modern train is quite unbelievable - just look behind the mirror on a 700 disabled toilet to see loads of electronics!!
As zwk500 says, the cost is negligible in the grand scheme of things - especially as modern trains will have network connectivity for its own systems and diagnostics. The amount of kit on a modern train is quite unbelievable - just look behind the mirror on a 700 disabled toilet to see loads of electronics!!