In the description of the Siren V2, it says Quad air slots ?? From the pictures provided, I see 1 air slot on the base with about 4 air holes in it that can be adjusted.
As far as whether the Siren V2 has a defuser or a air plug, I'm hoping that it has the same defuser as the V1's do. Why ?? If one is a Tight MTL'er like me, then it will matter which way Digiflavor decides to go on this. A defuser, like in the V1, defuses (spreads out) the air across more of the bottom side of the coil (to also cool it) than a single tiny hole would. I have the Coppervape SkyLine, and in
it I have put in the air disk with the smallest single hole that they make, which is centered beneath the center of my coil.
What I have found, is that I get almost half the wick longevity as I do in my Siren before I get that off taste and have to change wicks. What I find is a scorched wick (on the bottom, in the center), even though I have 1 of the 2 air slots fully open on my SkyLine. I'm guessing that not enough air is getting to enough of the coil to keep the wick cool (except for a little spot dead in the center of the coil) and the heat of the coil is singeing the wick from almost the first hit. The folks that use more air don't have this problem near as much as us Tight MTL'er's do. The air supply under the coil is not only for tightness of draw, but also (and primarily) for cooling the coil that is touching the wick so as not to burn the wick in two from coil heat. For we that like a tight draw, this becomes a very interesting dance of air circulation on the coil/wick versus Draw comfort, and I think that a defuser would be more efficient than a single, tiny, air hole. That's my

anyway.
Edit: I have also found this to happen with my Taifun GT V2 and other RTA's that I fit with a smaller air tube for under the coil to tighten up the draw, so not specific to just the SkyLine. My Coppervape Hussar I have the 1.3mm air tube installed and have no problems with burnt wicks, so I think it might be partly the design of the air path also, but just my guess on this one.
I think they mean 4 air slots instead of one air hole under where the coil sits, as opposed to the AFC ring on the outside of the tank. In prototype pics I saw if the V2, that is how the base looked below where the coil sits - 4 long, very narrow air slits. I'm glad they have kept that feature from the prototype, as I agree with you about the Siren's MTL airflow using that cap - instead of just a narrow hole. I think the 4 slits might actually work better than the cap. We'll see.
You are about the first that I have seen post that SS 316L doesn't work smoothly in TC mode. I'm curious as to how it doesn't work smoothly for you. I have never used SS wire for anything myself, but in the posts I have read about SS wire, I have never heard this complaint, or in fact any complaint, about SS wire being difficult to use, or having any sub-par results in TC mode. I've always read posts saying that it has been better for TC than the rest of the wire options. So, what's going on billy that SS wire isn't working for you (I've been back and forth on getting some 316L myself for experimenting purposes, that's why I ask).
It depends a lot on the quality of chipset your TC mod uses. A DNA 75 device I have (that I sadly think is just too large, so I don't use it much) runs SS wire fairly smoothly, or at least smoothly enough for it not to be a big issue. NiFe30 runs better though, because of its TCR allowing for more functional accuracy.
The TCR of SS wire does not allow for as much on-the-fly operating accuracy compared to wire materials such as nickel or titanium. So, if you are pushing things a bit, for performance (like I do frequently, when I MTL chain vape), then the chipset of many TC mods cannot keep up with the rapid changes in coil resistance that it uses to guesstimate the actual coil temp.
Remember, the TC mod is only making an algorithmic guess, based on the wire's TCR, about what the wire's actual temp is. SS wire doesn't change its resistance much (at all) as it heats up, so it is just that much harder for the mod to properly adjust power quickly compared to if you were using wire with an easier to read TCR.
Kanthal A1 has an even harder to accurately read TCR, which is why it is never used for TC builds. SS and Kanthal wire have TCRs that are fairly close compared to other wire materials used for TC. Nickel is very good, as its resistance changes a lot, and quickly, as it heats up, which makes it easy to read and adjust power for by you average TC chipset. For a variety of reasons, mainly because it is very hard to work with, nickel wire is not optimal for building TC coils, though plenty of people still apparently use it for that.
Nickel and titanium wires produces toxic chemicals when they are super heated, which will happen if you dry burn them. Lots of people don't want to be concerned about that (understandably), so they just use SS wire instead, which can be dry burned without creating toxic chemicals.
Depending on your needs, SS wire for TC can be just fine, but I don't think it is working that well for me. It just works "okay". It is easy to work with, and doesn't cost that much, but that's about it. Those aren't bad things, but they are not great either. I may or may not like titanium better. I'll just have to wait and see.