Jace would absolutely see play as a 2 mana free looter each turn. Nissa, not so much for a 3 mana basic forest fetcher.

The difference isn't whether or not the creature is playable at all... the 3 playable cards all have internal synergy or protection - on both sides. Lili and Chandra really don't. Chandra isn't terrible on the front, lili really is though. Will she ever be playable? Possibly. I can think of hypothetical decks that could use her, but it's not at all obvious. Her back side is very good though.

Lili is actually easier to flip than jace btw... the issue is that Jace can flip himself, and she can not.

Of course it is. You can't put a PW on the back of a 5 mana vanilla 1/1 with a ludicrous flip condition and expect it to be good, no matter how amazing the walker side is.

Nissa without the the walker side would still be close enough to Civic Wayfinder/Borderland Ranger (both cards that saw significant play in their Standard formats) to still be a fringe (very fringe) playable, and way closer to anything playable similar to Liliana and Chandra. Just compare Liliana to Vampire Nighthawk.

I think it's fair to judge the other flip walkers by their creature side value, but what makes Liliana better than that is her flip condition. A 2/3 lifelink for 1BB is of course terrible. But her presence on the field paralyzes your opponent's defenses. Even if you don't have sac outlets to flip her, you can force damage through that you otherwise wouldn't because they don't want to kill anything.

*gasp* You're right! I have to think for 2 extra thirds of a second before using Harnessed Lightning on Liliana instead of some other dumb creature.

Duels desperately needs a symmetrical draw effect for her discard effect to be truly effective late game as well.

We need something like Fevered Visions.

Well, fwiw, I think the rest of the post was pretty important here - specifically, Nissa etc... have internal synergies with their own flip conditions.

On the subject of Wayfinder and Ranger - they are both better front side cards than Nissa - unless the deck is mono green. Nissa only tutors basic forests, I don't think her front side is even fringe playable in Standard on its own. The fact that her front side synergizes with her flip condition is, IMO, WHY she is standard playable. Lili doesn't have that or she would be playable. For example, if lili had a way to sacrifice a creature printed on her front, she would be totally playable.

Regarding a 5 mana vanilla 1/1, I certainly didn't suggest any vanilla flip walker would be playable. The post was pretty clear in that regard - or so I thought. I meant the card needed internal synergy with it's flip condition. A super easy to flip 5 mana 1/1 could still be playable depending on what the flip side was.

A UR 2-of isn't the greatest combo with a PW that requires BB, but yes, that's the closest thing we have. I'd trade a ball for Mikokoro, Center of the Sea or even Howling Mine tho. Just imagine how awesome Howling Mine would be with Improvise...

I'd love Howling Mine!

I doubt it, Jace would still be a 0/2 creature and looting isn't that important. It'll virtually never block; all it does is sit there improving your draws (and enabling graveyard synergies I guess). Compare Sigiled Starfish and Lifecrafter's Bestiary, both of which show up literally never, and Merfolk Looter. I don't know whether Merfolk Looter saw play when it was in standard, but I know I never read of it in coverage now. DJ0045 also makes a good point about Nissa's ability to fetch Forests. If you're able to cast Nissa, chances are you already have one Forest in play. The same doesn't apply to Borderland Ranger and Civic Wayfinder. With the exception of Kytheon, these cards aren't worth playing without the flip effect.

Liliana not being able to flip herself is a valid criticism of her. She'd certainly be better if she flips off tokens dying as well (e.g. Eldrazi scions). But we have alternatives that can help flip her. Let's ask the reverse question: if you looked at only the flip side, how would you rank the five flip walkers?

About the symmetric draw effect - do modern Jund decks run that, or is Liliana of the Veil just that good?

Doubt all you want, I would still run an 0/2 free looter for in a few decks. Not the control decks I'm used to, but there's plenty of Izzet builds that'd love it. It's miles better than Scryfish, since I get the card I'm after in my hand with the benefits of either being able to discard + madness cast it (the sort of build that would LOVE this nerfed Jace), or hard cast it if it's something I needed there and then.

I'd run howling mine with fevered visions!
All we'd need then is winter orb...

Lili is not that good; she's even better than that. Her +1 seems symmetrial but helps your deck quite a bit (Tarmogoyf, Scavenging Ooze); her -2 means she is a 2-for-1 at the very least and her ultimate (at -6! That's a turn faster than ultimates we know) is completely game over against anything unlucky enough to not be able to deal with her.

Compare with flip Lili's PW side. Even assuming you manage to flip her the turn she comes into play, she needs the same amount of turns to ultimate - and her ultimate is a lot less powerful because it's less immediate.
Also her -X takes up more resources to be good at all than Veil's -2, which is good whenever the opponent has a creature out. And it's -2; not even -X.

Even compared to Last Hope, Veil has the faster and more powerful ultimate (and Last Hope's ultimate already is pretty fast and powerful!) and her removal ability affects the board in a more meaningful way. If you want numbers: The Jund list I've consulted and every other Jund list I know of runs 4 Veils mainboard; this list is one of the few ones that runs 1 Last Hope sideboard.

There was a VERY good reason for her absurd price tag; and it will stay very high despite her reprint in MM 2017.

How my Temur Fog deck would love Howling Mine! Watch me take over the universe with the power of a howling mime!

Edit: In regards to Liliana of the Veil we should also keep in mind that when she was in standard it was during a block with tons of GY synergy and Flashback, and at that time the standard meta really tended to favor Control decks.

Merfolk looter saw play the last time it was in standard afaik.( mtgtop8 reports 10-11 apparences in standard events with some big names and events included, it was during innistrad so probably the merfolk by itself is fringe playable).

Tbh you'd sometime point a removal spell at jace asap even if the whole flip side was missing.
That's huge for a 2 drop that is relevant late game and gives you close to a card value if it survives 2 turns.

I think borderland ranger was mostly played in the unburial rites / angel of glory's rise combo, but I might be mistaken.