title_body: Is it possible to make a declension system that DOESN'T limit what nouns can end in?
upvoted_answer: Ignoring the lost natlang, I'll just answer the title question:
  
  There are several possibilities to let nouns end in any phoneme of the language and still have case inflections:
  
  
  Most simple: Have a zero ending in the nominative singular
  Base your inflection on prefixes (like in Bantu languages) or infixes (like in Semitic languages)
  
  
  BTW, inflections with thematic vowels (like in Latin and Greek) aren't particularly difficult to remember, because the thematic vowel is easily recognisable throughout the whole inflection paradigm.
  
  PS Many natural languages have only a restricted set of allowed phonemes at the end of a word. Classical Greek is an extreme example of this kind of restriction, but also German has Auslautverhärtung aka final devoicing: Final consonants are always devoiced. This feature does not show up in writing but only in the spoken language.