> I don't see why something similar can't be done for the Czech alphabet.
It probably could — we already can't fit all the letters with diacritics on the number row, so "ď, ť, ň, ó" are key combos. But as far as I know, Czech uses diacritics a bit more than Polish (e.g. for sounds that are digraphs in Polish), consider:
"Že se nestydÍŠ, nutit lidi psÁt ČeskÉ speciÁlnÍ znaky pomocÍ dvojhmatŮ!" — that's 10 modifiers just for the diacritics.
Having ALL diacritics as modifier combos would make typing actual texts even more annoying than programming is now.
Poland ditched a similar QWERTZ-based layout in favour of this: https://pl.wikipedia.org/wiki/Plik:Polish_programmer%27s_lay...
It's basically the standard US layout but the right alt (AltGr) is a modifier. So, for example, AltGr+A gives "ą".
I don't see why something similar can't be done for the Czech alphabet.