I was collecting a substantial amount of data about Slicing returns before the nerf hit, and since then I've been collecting more data to see what changed. Here's what I've figured out:

Lockboxes gained from slicing have two properties: a rarity (color) and an item level. The average number of credits gained from a lockbox depends on both of these. The item level of the lockbox is determined entirely by the mission level. (I.e., the class of the lockboxes as described in the mission). Class 1 Lockboxes are item level 10-16, Class 2 18-24, etc. The rarity of the lockbox is determined entirely by the yield of the mission:

Moderate: white box

Abundant: white boxes, green on crits

Bountiful: green box

Rich: green box, blue on crits

None of this is affected by the nerf.

As far as I've been able to determine, the types and qualities of lockboxes received from slicing missions is entirely unchanged. What has been changed are the returns from green (medium) lockboxes. Before the nerf, the quality upgrade from white to green increased the yield about 3-4 fold, which was generally a much larger effect than the effect of Class or item level. A white class 6 lockbox gave around 1700 credits on average, about the same as a green class 3 lockbox. That meant that it was always better to run bountiful and rich missions because you could be assured of getting the much more profitable green boxes. Post-nerf, the quality upgrade from white to green increases the yield about 50% or so.

According to the adjusted yields, most missions are still on-average profitable. What they aren't anymore is guaranteed to give you a profit every time you run them. Your four missions that lost you 1000 credits are a product of a random number generator that is balanced by some other guy who gained 1500 credits running missions, but isn't on the forums whining about it.

Before the nerf, the most profitable missions were estimated at ~5-6k credits/hr. After the nerf, the most profitable ones are ~1.5 credits/hr. They're also fixed so that higher level missions are generally going to give higher estimated returns, even if they're not Rich/Bountiful missions.

Also, slicing mission costs haven't been changed. I've got a list of all of them before the nerf, they're still the same.

TL;DR: Slicing is still (on average) profitable. Individual missions are no longer guaranteed to earn credits. Higher level missions are now more profitable than lower level missions.

Sure, it's profitable, but then so is working at Taco Bell. It's just not all that enticing an option. Running Salvaging missions and selling high level materials is definitely a more lucrative endeavor, on my server at least. Sure, you don't get the money as quickly, and you have to pay attention to the market, but that's not exactly hard work. Other gathering skills also have the plus of being able to support crafting skills directly.

Really, though, whatever. I'll just ignore the missions and use it to open boxes in the wild. It would be far too costly and/or time consuming to train up another skill at this point. From here on, Slicing will be the skill of choice for bank alts everywhere, but I doubt anyone else bothers.