1) Which of the currently proposed skills would you like to see alongside the Ballooner in 2.5?
*Probably Ladderer.
The Ladderer and the Twister / Propeller would be on par in terms of the "design gap" they would fill (downward Builder vs. upward Digger).
I would assume they take a little longer to program, though? Perhaps Ladderer and Twister should be introduced in the same (later) test version.
For right now, if the Ballooner is already finished, the Hoverboarder (as a simultaneous stand-in for Runner, Surfer, and "horizontal flier" skill) would probably go along with it nicely.Both the Ballooner and Hoverboarder are "flying" skills, but accomplish something quite different:
- The Hoverboarder can be isolated from a crowd horizontally, and lends itself better to flow-control solutions.
- The Ballooner lends itself better to classic "worker lemming" solutions, where the crowd stays behind, while the Ballooner goes ahead / up to carve out a path.
2) Are you happy with 28 as a proposed limit on skills, or would you like this to be lower/higher?
*I actually don't know yet. 28 sounds good, but I hate to place restrictions like this. What if we get the ultimate idea
for a skill, but we already hit our set limit?
I agree with jkapp here. There are too many ongoing discussions about potentially useful skills right now to already set a fixed limit.
The Hoverboarder has already helped to identify and eliminate some of the less useful candidates (Surfer, Runner, Magic Carpet etc.), by joining them all into a single, much more versatile skill.
So I'm not worried about us exceeding that potential limit of 28 too far yet anyway. However, precisely for that reason, I wouldn't set the number 28 in stone at this point. If we do end up with 30 skills in the end, for example, would that be so much worse? I don't think we'll blow things up to 40 or something.

3) Do you think we shouldn't add another skill, and instead cull a skill to keep the total at 24 (current Status Quo)?
I'm happier to see a skill or two added.
When in doubt, I'd always advocate for rather keeping the existing skill set than for adding two further ones in exchange for culling an existing one.
The latter option would likely taint the players' joy about the new toys with the grief over having lost a long-established skill. 
I can understand the changes from Stoner to Freezer, especially with the demonstration / introduction video that WillLem just uploaded.
While this does increase the challenge of converting old levels to SuperLemmix, it also might make some of them easier to execute (ironically, since SuperLemmix is perfectly fine with more execution difficulty than NeoLemmix

). For example, any level that requires Swimmers to dive under Stoners will be less pixel-precise with Swimmers and Freezers instead.
However, any further such changes would complicate any potential conversions of existing packs to SuperLemmix even further.
For example, if culling discussions were to come up, I could see the Stacker and/or Disarmer in danger next.
And I've spent too much time coming up with useful Stacker tricks over the past years to be ready to potentially lose the Stacker now.

While the Disarmer is more restrictive in its current applications, we have already discussed how some of the future objects planned for SuperLemmix might make the Disarmer more versatile, too. (For example, if it could disable radiation or slowfreeze objects.)
TL;DR: If there's an unspoken skill limit for SuperLemmix somewhere already, I'd rather see fewer new ones added than existing ones removed.