There's a lot of common sense in rolling this out (and hopefully we'll see more). Intercity trains must be one of the highest usage locations for MBB outside the home/office, so better coverage and capacity is surely a great differentiator. Also, it guarantees a great QoS in areas where MBB coverage is usually lousy. I travel quite regularly from London to Cambridge and the network coverage for large parts of that journey is non-existent. Finally it reduces the need for the network to cope with all those connection set-ups and tear-downs that must be a nightmare for network management.
Now, if they could only do something about those British Rail Sandwiches*.
*"Joke" circa 1983.