I'd be curious to see what unrestricted Necropotence could do in our current format. Naturally Turn 1 Ritual+Necro is very hard to beat, but it requires 2 cards and earlier you needed to have a Force to beat it. Now you can have either Misstep or Force. The later the game goes on, the worse it gets too, especially with the current format being very unforgiving on life totals.
Of course, I'm going to have people jump on this post and call me insane, or say that they cannot take me seriously anymore, or worse.
I'm not an advocate for unrestricting Necropotence, but it is an interesting thought experiment.
You are right to point out that just unrestricting Necro doesn't make it a reliable play. After all, Misstep is ubiquitous, and waiting to prevent early Necro from being cast. In addition, cards like Spell Pierce and Flusterstorm can also stop Ritual off just one land, and Spell Pierce can counter Necro directly.
Necropotence is especially risky against Shops now that Ballista exists. Revoker can name Necopotence proactively or reactively. Spheres will slow any combo player down. And Ballista + Revoker can take a huge chunk of life as the Necro player searches for mana and a Hurkyl's or other answers.
The one clear area where I think Necro would be very strong is against Mentor or other blue decks. I have a difficult time imagining that Mentor or other control decks would be favored there.
Although, I think we'd see alot more proactive Pithing Needles coming out of blue sideboards, and more maindeck Spell Pierces. So who knows? Maybe things would actually balance out?
But my best guess is that a 4 Necro deck would have good matchups against Blue decks, but weak matchups against Dredge and Shops.
It sound crazy, but maybe it's not insane.