Well, keep in mind, if not using a shotgun on a fishpole, or a close cardioid or lavalier, the "debate" you speak of will be a little distant and unfocused no matter what else you use.
I suppose you could try one crazy thing if you are not going to pursue mic placement, but positioning the mic will always get the better results.
Here's the half baked idea.
On ebay sometimes you see people selling auction "lots" of many Shure, Audio Technica, Beyer, Sennheiser, Crown, etc. PZM (or "Boundary) mics. These were typically used in conference and board rooms, or placed on tables and such at large conventions etc., to pickup every speaker at said table. Probably mixed in multi track later, or maybe just used for pa, although feedback would be a nightmare scenario live.
These do NOT have a wide freq response typically, are tailored for speech only and are a couple notches up from conference table telephone communications type omnis etc. Well, maybe a bit better than that.
The ones I have used and own however, are EXTREMELY sensitive, almost to a fault, and have a ton of reach, meaning they will pickup whatever from quite a distance.
Anyway, you could potentially grab one of these lots with like 8-10 pzm mics in them or whatever, and arrange them in "zones" around the room, record them to their own track, and mix them later. Arrange them so that none of the mics is too far from where anybody in the audience is sitting.
Later, on mixdown, you mute ALL other mics save the one that the speaking audience member was nearest at the time, and this could probably give you clean enough pickup to use. It's still never going to be as good as somebody pointing a mic at the speaker though.
That said, if I had no other choice, and I wanted to be covered, I'd maybe try this. If doing the recording by yourself for example, and you don't have the capability of making it to debate speaker #2 in time to catch his rebuttal, so something like this might be the only way to go?
A couple of lots here (see link at bottom), and some cheap deals.
None of the huge ones I had seen before though.
I once saw some crazy auction with like 30 of these AT mics.
You will have to experiment to see how far you can be in your room before the sound starts to suck, and lose intelligibility. This will tell you how many mics you need to cover the whole room.
Thankfully, there are some singles as cheap as $29.00. I have some Beyer models that are very good at this type thing.
Don't know how good the other cheap ones are, but that's probably used price to begin with, and you are not going for a studio vocalist on a U67 tone anyway right?
Good luck, hope it helps some,
john boundary mic | eBay