E-Sheep, yes, in terms of size, capability and cost Chinook/Puma or Chinook/Blackhawk is a more effiicient mix - but this has little bearing on defence procurement when a British (ish) company is involved. The compelling case at the moment is to upgrade the Puma - makes the support issues much easier - rather than introduce a new type, ie Blackhawk. A combination of re-engined Pumas and Carsonised SK4 will let us limp to the ISD of a new type in the 2015-2025 timescale (funding permitting).
Converting the Mk3 Chinook into MH-47E/G is not straightforward. We would run into all sorts of IPR/ITAR issues, not to mention having to attempt to certify the Rockwell cockpit which contains SOUP. Therefore, back to square one!!
The extant Mk2/2A fleet will require a further MLU in the next decade, where, I'm sure, a lot of the digitization issues will be addressed.
The 412 has much merit as a stop gap, esp as we train pilots on it already. However, having sampled it in a variety of military guises, it really is no long term solution. By the time you've armoured and DASed it up you're left with very little performance - Why do you think that the Canadians have not taken their CH-146s to Afghanistan?
The MoD and politicians owe us new helicopters; at the very least they should back up this "extension" of existing types with real money in the future and open competitions to give us what we need.
One very real problem we face is a reluctance on the part of industry to bid for Helicopter programmes in the UK, due to Westland's lobbying power. Understandably they don't wan't to waste millions of euros providing products/briefings/corperate entertainment if the UK Govt instinctively props AW up with contracts.