The Germanic Ethnicity of Isolde, the Goddess Isa and Iceland

In my researches into Germanic mythology I occasionally find references to a rather obscure Germanic Goddess called Isa. Isa as we know is the name of the 11th rune of the Elder Futhark, also known as Is in the Anglo-Saxon Futhork, Iss in the Scandinavian Futharks and Is in the Armanen Futhork.
There is a theory that this Goddess lends her name to Iceland or Island.
"Rassmann identifies Island as derived from Isa, a goddess of the under-world, probably the same as Holda, and not as Iceland."[Legends of the Wagner Drama by Jessie L. Weston]
As a female personal name it is Teutonic and of ancient origin, signifying aristocratic, strong willed, a ruler. The element of strength is brought out in the hard, icey and cold nature of the Isa rune.
It is generally considered that due to the Celtic location and time frame of the Tristan and Isolde legend that Isolde was an Irish Celtic princess. However this is a mistake albeit an understandable one.
During the 9th century CE it was a Viking and not an Irish king that held court in Dublin and we should not forget the significant Scandinavian and thus Germanic heritage of Ireland from the 9th and 10th centuries.
German scholars according to Jessie L. Watson derive Isolde`s name from Iswalt or Iswalda[Eis-walterin=ruler of the ice]. The earliest form of the Isolde name is Isalde[Wolfram von Eschenbach]. Legends always represent her as fair haired-`die lichte` as opposed to the rival dark-haired Isolde. She concludes that the Germanic forms of the name have more in common than the Kymric Essylt.
It is also interesting to consider that in the German Nibelungenlied Brunhild is represented as the queen of Iceland and her very nature is hard, icey and strong-willed. She dwellt in her fortress Isenstein[`Ice rock`]and was a beautiful woman of formidable strength and fortitude.
Could it be that the two distinct legendary figures of Isolde and Brunhild originally derive from a common Germanic source?