I started mixing in anal every now and then -- she was open to it and of course I loved it. We got into this pattern where the plug would be in her backside while we did our usual vaginal+vibrator sex, she would have her orgasms, and then it was my turn. More often than not I would pull out the plug and fuck her in the ass to finish. She was accommodating but not really into it; by that point she was done.
Then a few weeks ago based on my reading here, I told my wife we should try something new, and that is for me to be in her ass when she uses the vibrator to come. She was skeptical but she went ahead with it. As I talked about in another thread, this was a HUGE success. She told me she had the biggest orgasms of her life. I took the opportunity to quiz the hell out of her.

Ever since then, we've done anal every time we have sex. And every time she is having orgasms! (I can feel her anus contracting around me when it happens, it's so awesome.) After so many years of marriage I am almost embarrassed to report this, but last weekend we had our first simultaneous orgasm! She was really excited about it, we both were.
I don't know if we'll ever be completely anal only -- maybe we'll get there -- but it feels like her consistently having these orgasms is a huge milestone.
Thoughts on where to go from here? I imagine the next step is to start skipping the vaginal every now and then, and go straight to anal.