The Structure stack is definitely one of the least cluttered and fastest grid stacks on the market. So I think if there’s any stack that could do a responsive grid within a grid then this would be high on my list for sure.
That said, I would recommend really taking a step back and thinking through this. If you have a 4x4 grid and each of those has even a minimal grid (say 3x3) then suddenly you have 144 responsive elements on your page – each one, presumably, with some interesting content in it. Even without JS that’s asking a huge amount from your browser’s rendering engine – older mobile devices will be slow if they render it at all.
If you really really really need to display so many things on the same page all at once and all responsive – then I think Structure is a good choice. But maybe see if there’s another way to skin this cat – if there’s some way to keep it simple – it will make your life much easier – and make the page load much faster. And faster loading pages are always always always ranked higher. Worth it.
Thanks for the comprehensive response isiah, much appreciated. I’m nesting a 2x1 grid inside one ‘cell’ of a 1x2 grid so I don’t think it’s going to be a problem. It feels a bit ‘tacky’ what I’m trying to do but I don’t see any alternative method for what I’m trying to achieve. I’ll test it on my mobile devices and see how it works…