I don't know if I'm reaching the capabilities of CustomLayout or not but if there is a significant amount of html being rendered (such as a table with a ton of data) then it seems to start to run into performance issues. Again it could be that the data I'm trying to push out is too much for the browser as well but do you have any estimation on how much data the component could potential handle before it becomes problematic? I ask because pushing the same amount of data into the grid without pagination seems to be fine. But that being said I suspect the grid component is not pushing all the data all at once either and is injecting data as needed.
It should handle raw HTML very well (limited by amount of transferred data and the html rendering in the browser), but in case you have a lot of components inside the layout, it might get more expensinve. I did some tsts a while ago, but don't remember how much it handled easily.
Grid scales much better indeed with big data sets, even without server side lazy loading, as even with in-memory datasets, only the visible rows (and some cache) is transeferred (and handled by the client).
Upon further investigation it looks like the issue was that I was pushing it in development mode rather than production mode as part of my testing. The difference is quite significant, much more than I suspected.
It's a great addon with some great features. Continue the great work.