A lot of talk on here about capacity uplift seems to assume captive services will still run. Maybe you'd better speak to the posters concerned. HS2 has little connectivity to the rest of the network. Trains will run off one branch towards Liverpool and Scotland, and off another on a short branch ro Sheffiled and towards Newcastle, and that's it. No additional connections to the south, south west of east. Some extraordinarily myopic features built in eg no northward connection to the line from Sheffield, despite the Sheffield-Leeds service being one of the worst between nearby major cities in the country: no Birmingham-Liverpool HS2 service, leaving instead an almost-all stops service taking 1 hr 45 mins to cover 80 miles. Your worries about adding to the cost of HS2 somewhat miss the point. We should be working out what the most urgent problems on the network are, and addressing those. Funny how cost is always wheeled out as an excuse not to do something which deviates from the current HS2 plan, and yet HS2's proponents seem entirely comfortable with the astonishing growth of the cost of fulfilling the current plan.