I don't have any suggestions for improving Armenian, but I think that the Latin alphabet should rip off letters from Cyrillic, or otherwise add new ones, so as to have as many as Armenian does - in order to be able to represent the additional consonants found in Eastern Armenian and Chinese that currently have no equivalent in the Latin alphabet.
The basis for this is that using diacritics instead to transliterate Chinese, at least, has tended to prove unsatisfactory in practice.
There's no reason, though, for the Cyrillic and Greek alphabets not to also attempt to grow in this direction - so as to make every script capable of competently transliterating every language. Of course, isomorphism would cut two ways, as while it would make every script suitable for quoting from other languages, it would also reduce the barrier to switching to a dominant script.
The good news, of course, is even if letters allowing Armenian to be written in the Latin script were in some sense "added" to it, since they're not needed for the languages now using the Latin script, they wouldn't be used enough, or available enough, to create any real threat to the Armenian script.