I also have a lot of concerns over Win10, the only reason I looked at it was DX12 but I am going to hold off till I know more. Either its free to get you locked into their marketplace or subscription based models, or there is other more sinister things as FalconFly eluded to. I don't know but I am cautious by nature.
I don't believe ED will support DX12 for a long time at any rate, so no reason to step up from Win7 for me.
It's a free upgrade for consumers so Microsoft doesn't have to support old versions of their OSes any more than is strictly necessary. They've never made any money from people upgrading, *that's* why they are giving the upgrade for free. There is no subscription model at this stage and if you take the free upgrade you'll *never* have to subscribe for your current PC.
MS is simply following suit and behaving like every other OS maker in the world - allowing paying customers to get upgrades for free. Just like iOS, OSX, Android, etc.