I find myself thinking: but how has English managed without a plural plural? The plural of horse is horses; but a larger grouping of a dozen groups of horses would still be horses. Why not horsess? Or horsesi. Or horsesim.
That said there are, as it happens, certain words that do seem to suggest plural plurals: one agendum; several agenda; the filing cabinet was full of many different agendas. But couldn't this be rolled out across the whole language?