OK, see your point. I think – trying to rephrase in different terms, and making sure I understand.
In my proposed method you’d have to use a single bank (button row) for the pages you want to switch between quickly, which means you have at most 16 pages that you can interchange, as there are 16 pages in a bank. In that case you would have the percussion covered by a bank (row of buttons, i.e. 16) and the other three banks (3×16 pages) free for other instruments.
I can see how it would be beneficial to remove that constraint from the banks. That would allow you to stack stuff at random. You could work around that by muting / unmuting the bank, or have an empty page play in the bank (in the last position for example..) Remember though that only the pages within the same bank are mutually exclusive at playtime.
So it’s now not clear to me – do you want to freely "switch between" pages, or freely "stack content" of pages – or both. My impression was that you area after switching, which means we need to stay within a bank.