Iceland has been crossed coast to coast N-S, E_W, NE-SW, NW-SE on skis. All groups have used bridges and existing infrastructure where that was logical. Somehow I have the feeling that those who did not speak English as a first language fared in general a little better on those crossings (they were better skiers).
No-one has bothered weather they stored or bought food&fuel along the way, -after all substantial parts of the coast to coast routes are inhabited.
The only „coast to coast and across the highland“ crossings in the dead of winter have been done with 4×4 on low pressure tires, -not skis.
The first coast to coast ski crossing were done a long time ago and I don´t know of anyone that has listed it up. This is old news and has been below radar for a long time.
In dead of winter there is usually little snow, many rivers are open, weather is usually bad and days are short.
If you plan to cross the interior highland on skis in dead of winter and are obsessed by doing that „unsupported“ I recommend the following:
-Do not inform anyone here about your plans. -If you are focused on survival, get info, permit and keys for all highland huts en route (-unsupported?).
-Practice building and living in snow shelters made on flat land. -Remember that you can not count on snow for shelter at that time of year and you can expect extreme thawing in gale force wind and rain. Igloos are useless.
-Tents have proven unreliable shelter for the worst winter storms.
-Sturdy shovel, wool and 100% waterproof fisherman bibs and jacket is the cheapest live insurance. You can expect gale force winds and rain&sleet for days.
-Use satellite tracking observed from UK only.
-Don´t call for assistance and don´t expect assistance.
-If you call for help, -be insured.
I wish you good luck for that project but I guess most locals don´t want to hear about it until you finish the tour. There have been to many blunders of this type in recent years.
Remember that „good luck“ in Scandinavian expedition history is directly linked to good preparation and experience.