Marco, you are not in the hardware sales business - you are a service provider.  I have a contract (actually three) which says exactly what the terms are, and you are perfectly within your rights to stick to the letter of the contract.  On the other hand, as a service business, GM will live or die on its reputation.  The way things stand every single contract in the past, and certainly every contract you make in the near future will expire with negative returns.  You may not admit this publicly, but I am sure you are an intelligent fellow and you can see what the numbers are.  I am not saying that exploding scrypt mining difficulty is your fault, but having dozens or hundreds of pissed-off customers telling everybody who will listen to stay away from GM is surely not in your best interests if you truly want to build a long-term business.  Not only is it annoying for us customers to lose money, but ultimately it is dangerous for the survival of GM.  You say GM is operating on a tight margin and cannot afford to upgrade 'old' contracts.  But you are also boasting about opening a huge new data center in Europe.  I think this does not come cheap.  Maybe you should think about re-balancing your priorities.  Better for your long term business survival to expand a little more slowly and gain a reputation for doing the utmost to look after your customers. 

I have made this suggestion before, and I am making it again.  Make it your policy to upgrade EVERY customer by a meaningful amount when you drop hash prices.  If that means fewer data centers and a few more years before you buy your megayacht then it is a small price to pay for survival.