Fjallandic is a partial worldbuilding/partial thought experiment on how a language or dialect of Old Norwegian might arise in (partial) isolation. Fjalland is a fictional region northeast of Trondheim that, like Elfdalian, preserves several extinct Old Norse features while innovating new features.
Some of the features of Fjallandic are discussed below:
Like Old Norse, Modern Fjallandic has only three regular vowels in unstressed positions – /a i u/. Most traces of Old Norse unstressed vowels have reduced to schwa or syncoped entirely. These new vowels are instead from sequences that contain two similar vowels and either a nasal consonant or a dental fricative in between. (This was taken from ED with permission.)
Like Swedish and Norwegian, Fjallandic has a melodic pitch accent, but with three levels of pitch instead of two. The accentual distinctions will correspond with the former number of syllables that the word had, so that hoppət, hoppə (< hoppa), and hoppə (< hoppaði) can be distinguished by tone alone.
Similar to the insular dialects, Old Fjallandic would have had palatalized /k g sk > t͡ʃ j ʃ/ before front vowels, perhaps before the reduction of Old Norse unstressed vowels. In addition to the tonal system discussed above, this would keep a distinction between some words such as uɲə and uŋə (ON: ungi and ungu) with the assimilations nj > ɲ and ng > ŋ found.
Similar to Icelandic, Faroese, and Setesdalsk, Fjallandic will have breaking of Old Norse long vowels in stressed syllables, and perhaps some short vowels as well.
Fjallandic will have merged the genitive with the dative case, or replaced it with posessive constructions using prepositions such as til. The dative case will be preserved. I have also toyed the idea of innovating a vocative case in Fjallandic similar to how the vocative was formed in some central Scandinavian dialects, but I am only at the research stage at this point.