So a big part of the reason why people or anyone reproduce is to push the species or just the bloodline to newer better levels, or to advance. This ties in to the TRUE ORIGIN of Mighty Thor. As to why Odin laid with Gaea.
Based off the recent image shown of Odin and the Phoenix becoming lovers, the mother storm in Mjolnir is actually their daughter. This would give explanation(and I use this term loosely with this crap) for why the Phoenix is "afraid" of the storm. The daughter has a potential for greater power.
It would "explain" why the storm never escaped before as there's a love/hate relationship with Odin.
It would explain how Jane(I will not give Thor to her on any level her name is JANE) was able to do so well in her fight with Odin.
And explain why Mjolnir resisted even Odin lifting it.
This is just a theory but it does fit.
Interesting, and certainly possible. Or have Odin reveal the real mjonir is hidden in Asgard awaiting Thor as it has been for thousands of years. What we have been seeing was just a uru hammer (since Odin wields it a million years ago) that he imprisoned the mother storm in. He liked it because of its power, but couldnt control it. So the only enchantment he put on it was the worthiness one so no one else could ever wield it. All its other powers are from the mother storm. Thor just focused his own power through it for all those years to make it do what it did. Odin told him not to touch it because he knew he himself couldnt wield it, and had mjonir made for Thor but Thor picked up the wrong one before he could give him the real one. So that is the true mjolnir in the upcoming solicits we have seen.
Thats the best I got. And its still not good.