Is this doable? Personally i always try to go for DB armor/Nightingale as soon as possible with a new character but i'm prevented from doing so because i'll have to change my armor after only a minute.

I'd rather start out with something overpowered and eventually let the game catch up, kind of like how Unique Weapons worked in Fallout 3/Fallout : New Vegas

Is there any way to make it so?

I would second this request, having scaling quest rewards that make it better to complete the quest late in the game is a huge deal breaker!

Rather than having these items with fixed stats, and giving out legendary items that overpower a low level character would it be possible to replace the stats with % increases? This way the gear would scale with the characters abilities rather than level. Some gear already works this way - resists and skill enchantments for example.

I anticipate that this will be a very easy mod, and one of the first made once the CK is released.

There is a mod like this for Oblivion so it will most likely come for Skyrim too

Theres been a mod for Oblivion that made unique Items level with your character. So when you where at level 1 the weapon would be at level 1 too.
When you got to level 30 the weapon would advance to level 30 too.

This was an essential mod for Oblivion.