I'm not as familiar with the K-3, but I think there can be problems with renewing the EAD if you haven't shown you've filed for AOS.
I'm thinking that you're thinking that if you divorce, and you haven't filed for AOS, you'll be able to send her back to India and she won't have access to the American courts to get your money. It's not necessarily quite that simple. Lemme explain where I'm coming from on this.
The VAWA (check out the FAQ at the top of this forum,
this question, specifically.) provides for foreigners whose spouses are refusing to file to file on their own. It was put in to prevent abusive men (not saying you are, mind) from holding the green card over their foreign wives and making them feel like they have to stay in an abusive situation or be sent home. (Blah, blah, yes men can be abused, too, consider that implicitly in there.)
The thing is, the law is (rightfully, to my mind) drawn very broadly because they'd rather err on the side of caution than not. So, it's conceivable that you'd initiate divorce proceedings, and she could claim emotional abuse, manipulation, and that you weren't filing the green card as a test for her.... and now not only is she still here in the U.S. to fight for her rights in divorce court, she'll be über-pissed and you look bad. (It's not an easy road for her by any means, but she'd be *here*, not in India.)
As far as the I-134 goes, it's not legally binding. The I-864 is, and it's a serious commitment, but probably the least of your worries if you're in a nasty divorce. Divorces aren't instantaneous either, and as long as you're still legally married, she'd have the right to be here.
I don't know much about divorce law and whether your hypothetical future earnings would be on the block, or just what you made during the duration of the marriage, or some percentage. But if you want to do a 'post-nup', you'll have to get a lawyer and that's what lawyers are for, to figure those things out. She'd have to sign that though, but there are ways to frame it so you don't look like you don't trust her; the post-nup can protect her assets, too. I have a good friend who is trying to broach a pre-nup with his (American) fiancée, because his family is wealthy and he stands to inherit a lot, and his family worries about divorce. They're not particularly romantic, but they are common.
Bottom line is, I don't think delaying AOS gets you any more security as to what she could get out of a divorce settlement.