Its just that - estimation based on diffculty.
But as difficulty supposedly is adjusted in order to keep ~ same amount of blocks per algo, its just an estimation.
Also in-wallet networkhashes are estimates. Cryptocoins are decentralized (Surprise!), which is also the case with mining. The network does not know who is mining until a block has been found by the miner. All are guestimates, if we knew how many hashes would be on a network jump pools would have not be a problem for so many coins.
Any work towards some way of getting network hash (via wallet)
Nope, but feel free to send in a patch.
getmininginfo is supposed to return network has after all :/
And why would that supposed to be?