title_body: Would these features be naturalistic in this scenario? Background
  
  I am planning a naturalistic Goidelic language which shall have quite an influence from Old Norse – probably at least 1/4 or 1/3 of the vocabulary to be of North Germanic origin, as well as a mostly undecided, but lesser influence on the phonology and grammar. Despite the North Germanic influence, I would still like to retain a ‘broad-slender’ vowel system, lenition, eclipsis, and (possibly) prothesis.
  
  Also, although I intend for the Old Norse influence to be less focused on grammar, I came up with the idea of, instead of deriving from the Old Irish definite article in and having it work similarly to the other Goidelic languages, I could derive from the Old Norse clitic article -inn and instead use this style of clitic article.
  
  Questions
  
  
  Would the retention of broad-slender vowels and consonant mutations be possible and at least somewhat naturalistic in this scenario?
  Would the replacement of the Goidelic definite article with an Old Norse-style clitic definite article be possible and at least somewhat naturalistic in this scenario?
  
  
  As an extension to this question – would it be realistic to retain the different Old Norse articles for the different genders (-inn for masculine nom., -in for feminine nom., and -it for neuter nom.) as well as the different cases (for example, -innar for feminine genitive singular) or to just keep one or two articles (such as to just derive from -inn for all the definite articles in my language), regardless of the gender or case?
  
  
  
  Thank you in advance.
upvoted_answer: Yes, the whole thing looks naturalistic.
  
  ad 1) When you assimilate the Old Norse words to a Goidelic phonetic system, lenitions and broad/slender distinctions come in very naturally. It will be more difficult when you insist on some Old Norse sounds sticking out of the Goidelic system; they can form exceptions to the lenition rules or evolve specific lenitions of their own.
  
  ad 2) Retaining the Old Norse suffixed article is definitely an option, and simplifying it to only one form (independent of gender, case, and number) looks most natuaral to me, but keeping the inflected forms is also covered by your artistic license as a conlang author. Or you may inflect the definite forms according to Goidelic inflectional rules.