I wonder how heterogeneous lists/grids will be handled though.

lots of ways to skin this cat, but for some inspiration, consider:

HeterogeneousList(data)  { item -> when(item.type) { ... } }

and for grid, something like

Grid(rows, columns) { row, column -> ... }

Of course something truly general will probably have a lot of configurable options, but it’s really easy to create some of these simpler overloads if it fits your use case, cleaning up code significantly.