Suppose Mamluks culture-convert a province to Turkish. Then that province gets conquered by a third country which is not the Mamluks nor the Ottomans. Years later, since it's Turkish and Ottomans are the primary nation of Turkish, that province gets Ottoman separatists when it shouldn't. The same would happen if Mamluks had Circassian as their primary culture.
I think Mamluks should have Mamluk as their primary culture, but all of their starting provinces should be Egyptian and Syrian (and both should be accepted cultures).
True. But if a culture is accepted by an AI nation, usually AI does not try to convert it (See for example what happens in Lithuania or in the Timurid controlled Persia, or in the Uzbek Khanate.), also without the direct intervention of the player is really rare to see the Mamluks survive so long to be able to afford a cultural conversion... But in any case, in case of revolt, a territory with turkish culture and MAM core, if I remember correctly, would generate a Mamluk separatist revolt if the Mamluk primary culture is Turkish.