Ex foris

By IPA, it's this sound: æ, or, as I'm using it: ææ pronounced one after the other. No glottal stop, in violation of my own hiatus rule. Is this sort of exception plausible? Am not sure why a language, like Luganda or Attic, would develop to disallow two vowels in sequence, so it's hard to envision why there might be an exception.

The Attic methods of forbidding hiatus between consecutive words are interesting.

I've also invented a sort of double 'a' vowel with the 'a' from 'apple' or 'attic.' So, 'jaarsis' would be pronounced 'jah-arsis.' Would the disuse of consecutive vowels make the 'aa' unlikely? Would such a construction naturally suffer elision into a simpler form?

My constructed language forbids vowels from running consecutively. That is, there will always be a consonant between two vowels. Devised the rule on a whim.

Is it plausible? Can you think of any general principle of language which would prevent this from happening?