Well i cannot call your stance inappropriate or unreasonable, but i think you got that already
As far as lenience be concerned however, i believe it depends on your definition of it, context specific of course. In my mind, they are doing the right thing; it is in light of said "right thing, right way of approach" that i base my own remarks/leniency approach on.
They will be using this very engine for more games. According to a latest interview, in fact plenty more. It is both cheapest and most efficient for them to work these things out now, get them to a state deemed appropriate, so as to forgo needing to address them again come the next game, where 'x' or 'y' feature will be once more, impossible to be ported over. By developing whatever middleware required themselves and then reshaping the Linux client around them, they ensure more time can be spent in (future) games development and less on the technical aspect of things, the outcome of which you will be unable to gauge in any case. Whereas inversely, a game with obvious oversights or weak 'factors' really IS something anyone would tend to notice. And you will get that if they have to redo this for each and every future title
That does of course imply a conscious decision somewhere along the line, sure. Hence my saying that in strictest terms, no one could possible blame you, not per se.
In reality however..Linux can have Win installed on top of it, and as a backer, you could redeem your key this very instant, and enjoy the game just as everyone else. Does this rectify past events? No. Is it however a more thoughful, moderate response on your part? Definitely.
It is one thing to delay, no matter for how long, and another to forgo. Officially. As far as the former is concerned, i am personally lenient. Why? Because norms. Most people get it into their heads that KS pledge = rewards or fuck off. Reality is you help someone make something (and risk paying them for nothing). I do not contribute because my name will be on the credits. Or because i will get a special pet, don't even use it anyway. I contribute because i want a D:OS out there, playable.
Which brings me to the second point, again from my view obviously. We have barely three (semi-major-ish) studios making AAA "true" RPGs as we speak. Three*. Dedicated on titles that take years of iteration alone. Forget the developing part prior to that. I think they deserve a support, since lacking it, i will be back to playing nothing at all. That's why i pay. Could torrent and call it a day, any day.
So to recap, as long as:
A) They are making good, qualitative true RPG games
B) i have not the slightest reason to feel as if my money is unnecessary to them?
I can excuse. Plenty of scenarios where neither of the above held. Not here however
* plenty of peoiple would say they are far more than three. I beg to differ. Just me