To be honest, I doubt that Windows 10 will make a huge difference to the market until the Enterprise version starts making an appearance and even then it's likely to be slow to move given the huge effort in recent times that was put into getting the corporate world off Windows XP and onto WIndows 7 or 8. The lack of real movement in PC design would make it harder still as the corporate IT section will look to maximise the use of its existing tin, so it's possible that Windows 10 will only make it in as a possible replacement when the existing iron has reached its end of life. With Windows 7 still in extended support until 2020, you could see little change overall before then.
As for the home market, go fig. Microsoft have never been brilliant at predicting the next shift there - they got lucky a few times, that's all. Indeed forcing down people's throats could be a bad move, negating any benefit of a "free upgrade". I guess we'll find out for sure come next July...