Nynorsk, Nynorsk, what a wonderful smogesbord of red and pickled herrings.
I once heard a young lady speaking to a group of trainee interpreters from various countries. She tried to describe, in English, the development of Norwegian. They became very confused.
The confusion seems to be based around nationalist language campaigners trying to develop a 'real Norwegian' to get away from Danish and Swedish. As they were scholars this appears to have had a great influence on literary Norwegian. We have had spelling reformers in English as well. They tried teaching schoolchildren at one time using a different spelling system I believe.
After the personal union with Sweden was dissolved in 1905, both languages were developed further and reached what is now considered their classic forms after a reform in 1917. Riksmål was in 1929 officially renamed Bokmål (literally "Book language"), and Landsmål to Nynorsk (literally "New Norwegian"). A proposition to substitute Danish-Norwegian (dansk-norsk) for Bokmål lost in parliament by a single vote. The name Nynorsk, the linguistic term for Modern Norwegian, was chosen for contrast to Danish and emphasis on the historical connection to Old Norwegian. Today this meaning is often lost, and it is commonly mistaken as a "new" Norwegian in contrast to the "real" Norwegian Bokmål.
Bokmål and Nynorsk were made closer by a reform in 1938. This was a result of a state policy to merge Nynorsk and Bokmål into one language, called "Samnorsk" (Common Norwegian). A 1946 poll showed that this policy was supported by 79% of Norwegians at the time. However, opponents of the official policy still managed to create a massive protest movement against Samnorsk in the 1950s, fighting in particular the use of "radical" forms in Bokmål text books in schools. In the reform in 1959, the 1938 reform was partially reversed in Bokmål, but Nynorsk was changed further towards Bokmål. Since then Bokmål has reverted even further toward traditional Riksmål, while Nynorsk still adheres to the 1959 standard. Therefore, a small minority of Nynorsk enthusiasts uses a more conservative standard called Høgnorsk. The Samnorsk policy had little influence after 1960, and was officially abandoned in 2002.
https://en.wikipedia.org/wiki/Norwegian_languageI imagine the language spoken in the Orkney area would have reflected the illiterate Norse dialects of that period and would have been similar to that spoken in Iceland and the Faroes.
In moving westwards Norse had to come to terms with other languages it encountered as well as the isolation it underwent as it became split from its original homeland. Norwegian at home had the influence of other Nordic languages to affect it. Once across the sea the settlers would have had to come to terms with others in order to understand each other.
In the Hebrides it merged in with the local Gaelic languages. On the east coast it would have arguably been affected with local languages which may well have had a Germanic base to them. In this situation it could have survived as Norn.