That isn't where it separates, a few news sources have got that wrong.
The junction is at the north end of the Birmingham 'delta junction', so that puts it in the right place to head up the M42 corridor in the general direction of Nottingham.
http://www.dft.gov.uk/pgr/rail/pi/highspeedrail/hs2ltd/networkoptions/pdf/report.pdf
Page 11 onwards
I've had a look at the potential route. The M42/A42 section looks like it gives good access to Nottingham. It's a pity that rebuilding Victoria is not an option, otherwise there would be at least a partial north-south route through the city with a station in the middle of it. Picking up the A453 would give access to the alignment north of Ruddington, and I suppose a massive tunnel under the city, surfacing around Bulwell, is not an option. Still, the GCR does present a possible alignment on towards Darnell, accessing Sheffield from the east, but that's not well suited to a route northwards (my version had a triangular junction here, but the main line would have gone via Woodhead). I suppose you could head in the Barnsley direction, but it might be easier to use the Meadowhall route, but that's harder to access from a GCR alignment. The Midland "Old Road" might be a better bet (as usual, not following exactly, because of curvature problems).
Looking further on, the quickest way from Leeds to Newcastle is via Ripon, but I would still go via York, giving passengers down the eastern side of the country at least some benefit from the route, by being able to access it there. Yet another use for cascaded Eurostars, which are of course cleared to work the ECML as far as York.
The journey time comparison on page 20 makes interesting reading (although I think their figures are slightly out).
London-Newcastle
- S - 3hrs
- Y - 2hrs 37
- Current ECML - 2hrs 51
- ECML fastest service - 2hrs 45 (I think)
- ECML record - 2hrs 24 (I think)
London-Edinburgh/Glasgow
- S - 3hrs 47
- Y - 3hrs 47
- Current ECML - 4hrs 21
- ECML fastest service - 3hrs 59
- ECML record - 3hrs 29
I reckon that IC225s running at 140 could equal, or even beat, the fastest times compared with HS2. If they extend the arms of the Y, even if only to Newcastle in the east, you really would get significant time savings. Do it by running parallel to the ECML, possibly closing the slow lines south of Northallerton to make space, straight through Darlington (potentially to access the station Ashford-style), then diverting roughly along the route of the Leamside to avoid Durham and rejoining somewhere around Pelaw Grange. I'd think about going under the Tyne rather than over, with a new station underneath the old, then surfacing somewhere around Benton (expensive, but saves on having to expand and realign the KEVII Bridge). Then, you'd be talking about reaching Newcastle in around 2hrs 10 or less.
As for Scotland, the difficult bit would be getting out of Manchester. By rejoining the WCML somewhere north of Preston, then running on a not-exactly-parallel route towards the Lune Gorge and Carlisle, then over Beattock to Carstairs, you would have the option of using the existing line to Edinburgh (at least temporarily) and a new line to somewhere around Motherwell, then the old line to Glasgow Central. Alternate services between Edinburgh and Glasgow, with at least some of the Edinburgh ones going on to Aberdeen or Inverness, and there you are. Then you're talking about a three-hour or less service between the capitals, within the famous barrier.
Of course, this doesn't deliver the 200 mph trains running into King's Cross, St Pancras, Euston and Paddington from different parts of the country that I wanted to see (especially King's Cross). We may have to wait thirty years for that.