One of the most important considerations is your player group. This method would require quite a lot of maintenance and book keeping on the part of the player. Would your players welcome such a complication to keep track of or would it be a burden?
You know your players, so don't forget about the impact this has on them in this decision.
I second this. If your player(s) aren't on board, then youmade things complicated for no real reason.
The option of changing domains on a short rest is still complicated. Imagine changing from Light to War. A lot of features change, such as Warding Flare to bonus action attack, an AOE Channel Divinity to a +10 to hit, etc. Keeping track of all that is a pain (let alone mastery) and what about things like proficiencies? Do I lose/gain my heavy proficiency as I switch? Making that change on a Long rest might be too much, and while I agre, making that change per level might be too infrequent to capture the feel, it still might be too complicated in play.
The *best* option is have a "new" domain, lets call it Norse Pantheon (you could have egyptian et. al. in your world too) that grants all the things you are looking for:
1) an expanded spell list (this is actually easier to change on short rest, so maybe the bonus spells 'known' are fixed per long/short rest)
2) Proficiencies suitable to the norse (no heavy armor, for example)
3) All the 1st level domain features and channel divinity available, but share the same use (Channel divinity is set, the other feature is usually wis mod times per long rest)
4) As the cleric levels they get to pick an choose higher level options from any domain (such as potent spellcasting or Divine Strike etc) thereby specializing and differentiating
The added flexibility makes clerics stronger, so consider using Piety for all the gods. Here you can add complexity, but its on your (the DMs) side: They gain lose points of piety as the serve or fail to serve the specific deities. A good cleric tries to appease them all, but often, the gods oppose each other so a cleric pleasing one, displeases the other. Access to domain spells (by level) or features can be a function of Piety, giving some measure of limitation.