Hmm, honestly, ZeroRecoil; the truth is, I have been thinking about similar things to the ones you mentioned. In fact, I think we could be right about something.
First of all, it called my attention the picture with Ben's Incursian form. I thought the same thing as you: if this is a new alien form for Ben, then where on the Earth is the Omnitrix's symbol? Every single alien form has the Omnitrix's symbol in some part of its body. Then, I though the same thing as you; maybe Incursian-Ben knocked out one of the Incursian soldiers, took its uniform and use it to infiltrate in the enemy's lines. Since the "green-pupiless eyes" are another sign of every alien form Ben uses, maybe that's the reason why he's using the sunglasses, to hide the other sign that can reveal his real identity. Actually, a pretty good plan to come from Ben; although he did something similar back in "Too Hot to Handle", when he used Water Hazard's form to impersonate Bivalvan to trick Pandor. Ben's really getting cunning... sometimes.
The truth is that I have been thinking about the idea of Ben getting an Incursian form since a long time ago. You see, if the hero calls himself "Ben 10", I think the new alien forms he gets must come in groups of 10. However, some of these lists have never been "completed". You see:
+ Originals (10): Wildmutt, Fourarms, GreyMatter, XLR8, Upgrade, Diamondhead, Ripjaws, Stinkfly, Ghostfreak and Heatblast.
+ Original Bonus (9): Cannonbolt, Wildvine, Benwolf, Benmummy, BenVicktor, Eye Guy, Way Big, Ditto and UpChuck. (Eon's form doesn't count because he's not a real alien).
+ Ben 10000's aliens (8 aliens): Spitter, Buzzshock, Articguana, Atomix, Toepick, Shellhead, Snakepit and Sandbox.
+ AF New Aliens (10): Swampfire, Echo Echo, Humungousaur, Big Chill, Spidermonkey, Goop, Brainstorm, Jetray, Chromastone and Alien X.
+ AF Bonus (3): Lodestar, Rath and Nanomech. (There are 5 counting Rocks and Squidstrictor).
So, I have been thinking about "complementary alien forms" that Ben could have to fill the empty spaces in these lists. The Incursians are one of them, although I had some doubts with such ugly looks. Anyway, I think the Incursians have actually more natural abilities than just their tongues. You see, most of Ben's alien forms are based in other superheroes: Heatblast - the Human Torch, Spidermonkey - Spiderman (or its equivalent in "Marvel Apes"), Humungousaur - maybe the Thing, XLR8/Fasttrack - Flash... etc. So, which "superhero" could be compared with an Incursian? I have one: the Toad, from Marvel comics. OK, he's not really a hero, but a villain; however, I think it's the most suitable to give us ideas about which powers could have an Incursian. (I guess they depend so much of their technology and weapons that they have forgotten their natural abilities). Anyway, since they based of frogs/toads, I think these are the possible powers for an Incursian:
+ Elongated prehensile tongue.
+ Superhuman leg and tongue strength and endurance, agility, reflexes, coordination, balance, and leaping ability. (Obviously, leaping frog).
+ Regenerative healing factor. (They could, since they are constantly in battle).
+ Can stick to walls. (Adhesice mucus).
+ Ability to expel gusts of air from lungs. (Big "croaks").
+ Psychoactive venom secretion.
+ Paralyzing mucus secretion.
+ Adhesive spit.
+ Expert kickboxer. (You know, with leaping legs, strong leg's muscles, powerful kicks).
+ Acuatic abilities, expert swimmer and underwater breathing.
So, with all this, even although is a little gross, I think an Incursian form could be useful to Ben. It also got my attention the fact that this "Incursian Ben" looks much more "handsome" that the "standard Incursian". It's almost like the Omnitrix takes any DNAlien and "perfect it" in the best possible way. Just like when Ben scanned Liam and gained Kickin Hawk; and while Liam looks like a ridiculous mix between chicken and pidgeon, Kickin Hawk looks like an intimidating hawk with some rooster's features. I also think that "Battletoad" could the perfect name for this new alien form; but since it's also the name of another franchise with the same name (one that it seems a lame parody of the Teenage Mutant Ninja Turtles"), I guess they will have to use a different name for this one. Maybe "BattleFrog"? Not the most original variation, I admit; but I don't think there's a reason to complicate things unnecessarily.
By the way, where did Derrick suggest a romantic involvement between Ben and the Arc 3 villain? I would like to see it "in person". You see, I can't believe I'm actually saying this, but the very first time I saw Attea in her Omniverse's design, I thought she was actually kind of hot, for an alien-frog princess from another planet. And after seeing the look of Ben's Incursian form, I think that could be the perfect mate for a female Incursian like Attea. Even if Ben uses his Incursian form to trick and defeat Attea, something tells me she would still be in love with Ben at the end. (Or at least, with his Incursian form). Yeah, sure, she's a greedy "alien-frog warrior princess" obsessed with power; but she's also a teenager. And something tells me that, even between different species through the galaxy, teenagers share almost the same patterns everywhere. Now that I think of it, this could be exactly like Looma's case, when she fell in love with Ben (or at least, with his Fourarms form). Maybe this is the reason why they have delayed "Rules of Engagement" for so much time? Could Attea and Looma's crushes on Ben have something to do with the next arc? I think Derrick mentioned something about "Rules of Engagement" being related to the 4th arc or something. If I'm right, then I can't wait to see this.
Finally, I don't think Ben will be mind controlled here. Like I said in another topic, I also suspect that the rest of Psychobos' mind control serum will play an important role in this arc's finale, "The Frogs of War". I had doubts about if Attea would use the serum on Ben or on her father. However, since she seems to have been planning the whole thing from a time ago, I think the most logical thing to suppose is that she will use it on her father. By her last words in the episode "Vilgax Must Croak", it's obvious that she's planning to overthrow his father again, just like she tried in "Alien Force". And she claims to be "older and wiser" now, I doubt she thinks that overthrowing her father by force is the best way. I mean, if Earth is the Incursians next target, why would she waste the mind control's serum on Ben? Attea clearly knows that Ben will attack his father and his army to protect his home planet at any cost. So, she only has to wait for her chance, allow Ben to weaken her father, and then use the mind control serum on him; allowing her to overthrow his father and become the new empress of the empire. Doesn't sound this the most logical thing to do?
Well, what do you think of my "analysis"?