Wife forgot

Not sure if you said you have locked up before, but...

If chastity is what you really want, then get a device and lock up. Show her what you want and prove that it is real. You've already done the hard part by openning up to her. She can then choose to participate or not. I would give her time and avoid applying pressure. In the meantjme you can see what wearing a device is like and test whether it is truly for you.

First of all, it's good if she laughed and took it with humor 😀

Most of us, I think you too, long for a certain dominance in the woman who is supposed to keep us chaste. Dominance is not 100% linked to sex but can take place in various areas of behavior, including in the decision about things that the partner wants. Your wife seems to be more of a carefree person who takes a lot of things with humor? That might not sound so great at first if you're actually craving a bit of dominance, but it also means that the decision isn't "no is no" but oops, was there something else? Forgot it.
So something could happen, but I don't think she's the one who will actively pursue it. At least at first. Later? May be.

I definitely know couples where I observe exactly the same behavior from one partner when the other partner comes along with things that aren't quite everyday. These are usually partners who always have something they want, put a lot of energy (and money) into it and then lose interest very quickly, usually before there are lasting results. Always wanting, always doing but never to the end.
I don't know you, and I don't want to offend you, but please think about that honestly with yourself. Because the fact that your wife basically "smiled it away" makes me, as an outsider, suspect that she doesn't really take Your wish seriously.

And that brings me to @tincup's answer. If you really, really want to try it, show her that you are serious about it. How exactly? Of course I can't say that now. Good idea ist to first see if it's really something for you, try it out - but with her knowledge!
Above all, show her that you really want her on board because you are not just doing this for yourself but first and foremost for her. She should enjoy the benefits that your chastity offers.

And do that without pushing! Maybe good literature will help, and by that I mean "good" in the sense of mild, realistic, not to ideological. She doesn't seem to me to be the type of person who absorbs and accepts everything that is written? It would be nice if you read it together. This opens up completely different dialogues than the usual "let's discuss what I want" because you discuss something together that a third person wrote. This is especially important because in this way both can be against something that is written there, which in turn gives your wife the security that not everything that exists in the big wide world of kink will rain down on her if she does wants to go on the adventure with you.

Has helped me and my wife in many things. We've even discovered a lot of things that we both find hot and desirable - but would never live out in reality. Frees the mind, believe me.

Good luck!

So, my advice may seem contrarian, but I really don’t this it is.  Try to dig down into why you are interested in chastity.  Are you hoping it will spark a kink in your wife that will reignite her sexual desire?  Do you want it for yourself?  Is it coming to the front of your mind because you are learning you want to be submissive and would like to initiate a broader female-led relationship?

If you are hoping that she will spontaneously respond to the idea of keeping your dick under lock and key and that it will reignite her sexual fires, it think you have your answer. Not only does it not push those buttons, she forgot about it altogether.

If you want to wear it for you because it helps channel the energy that builds because of reduced sexual frequency, then go for it.  It sounds like she will tolerate it.  Just don’t expect that you having a cage on your privates will change her behavior.

If the urge for chastity is the canary in the coal mine of a deeper desire to change the nature of your relationship to an FLR, then stop thinking about what it takes to get your penis in a cage and start thinking about what it takes to show her the benefits of embracing an FLR.

In my experience, when it comes to the overlap of an authentic FLR and chastity, the chastity always follows the FLR, not the other way around.  In my life, I had an interest in chastity and realized that my attraction was based on having a constant reminder of my commitment to my wife in our FLR.  But my wife is not interested.  She likes the idea that reserve my orgasms for her pleasure because of my conscious 24/7 commitment and dedication, not because she forces me to keep my hands off.

I am permitted to wear my metal rings on special occasions for me, like on our wedding day or when she is traveling for an extended period and she knows I will long for her touch.  But otherwise, it is a bother to her and she just doesn’t believe that it is not uncomfortable.