I don't know if you can call it 'play' when you are only influencing if the accordion is sounding or not. I would call it 'listening' to accordion by resizing your browser window. I understand that if the user did have control it would not sound as good, but you could do it.
The size of the window vertically would control the pitch, so if I have a small sliver vertically it should be high pitched and if my browser window is tall(vertically) it should be low pitched.
The speed of the change in size horizontally should be how fast the air passes through the instrument.
If I have it vertically large and slowly drag it to the left it should let out a low drone, if I go quickly it should be a low burst, etc.
Resizing a real accordion only influences volume, i.e. the harder you push/pull the faster air flows over the reeds. And you inevitably get no air flow at all when you switch between pulling and pushing the bellows, so you have to time this right. It's a fascinating instrument.
And then make a litte plugin out of it, so this can be put on all websites; using a canonical CDN location would even mean everybody has it cached all the time, so there'd be no downside to doing that.
I have been wondering what the web 3.0 would look like for a while now, but I asked the wrong question.... what does it sound like, that is what matters.
My first impression was that Play related to the framework or just meaning something games related and that accordion meant the UI element e.g. http://jqueryui.com/accordion/. I think the title is fine, but I wasn't expecting music at first either.