Thus far it's primarily the Chinese teams running any sort of mass-Midas strat but it hasn't exactly been a winning one. One match had Rising Stars with a decent lead on DK early on, but they used it to farm like 4 HoMs, and it basically cost them the game.
I think it's going to die a pretty quick death once they go against the more aggressive Western teams who will easily be able to punish that kind of greed.
It can certainly be valid as a way to secure reliable gold and XP for a hard support, but you sacrifice a lot in early-game map awareness by not warding/counter-warding and also by not having your Mek/escape items built in time for early teamfights.
On mass Necro3, that's another story. I've read that in Dota 1 they would artificially limit the number of Necrobooks you could have per team, but apparently that is no longer the case. If it really does take off and nobody builds an effective counter shortly thereafter, we'll surely see some kind of nerf.
Personally, I think they are both fast-passing fads teams are experimenting with considering the possibilities afforded by the new patch.