I don't see the point of starting another room, as everything that's been mentioned here so far would fit in with The Biosphere. Here's the thing with chat: it is what you make of it, and the attitude of the participants is everything. I spend a lot of time in the Python chat room on Stack Overflow, and a conversation like this would be pretty much unthinkable there. Yes, random people come in and ask Python questions that may be off-topic on the main site, or too short, or whatever. However, a lot of the time the room regulars, and whoever drops in, are just ... chatting. We usually stay away from touchy subjects like politics, unless it's to make fun of somebody. We joke with and about each other a lot, as the regulars have spent so much time there that we all "know" each other (at least, our online persona, as real or constructed as that may be). The atmosphere is quite collegial, and we just generally hang out and have fun, along with helping random strangers (or each other) along the way with programming issues. There are a number of room owners, and a defined set of room rules/guidelines, so if anyone is really getting out of hand they can be pointed to the rules, and booted if necessary. Over-the-top messages do get deleted on occasion, but it's all done by ROs, not mods (although some of the ROs happen to be mods). We have cv-pls and dv-pls tags requesting close and delete votes, respectively, on specified questions. We talk about interesting questions, and discuss how to best answer the particularly thorny ones. We complain talk about our jobs and coworkers.
The culture in the Biosphere is much different. I don't see extended conversations that often, and if there are some, they're generally very "professional", even what I'd call uptight, at times. People don't relax in there, or banter, or make much of an effort to draw others out of their shells. Things just seem stiff, kind of like attending your partner's work cocktail party where you don't really know anyone. It's hard to explain.
I commend TanMath for trying to improve things, but it's going to take everyone coming out of their shells and really participating to make the room more interesting. One difference between here and SOPython is the amount of time people spend on the main site, which is directly related to the quantity of questions. From mid-morning to mid-afternoon US Eastern time during the first half of the week, the Python tags may get five or more questions per minute, so there's a reason to stick around for a while to see if something interesting comes along that you can answer. That means a lot of people hanging around, and chatting while they do so, and provides fodder for them to discuss. Biology gets five or so questions per day on some days (others are faster, I know), so there just isn't that much site-specific stuff to talk about. I do think we should be much more proactive about cv-pls requests (hint: type [tag:cv-pls] in a post or in chat to get the cool tag formatting) to get rid of the garbage earlier. If it's obvious that something needs to be closed, don't be shy about spreading the word!
So, what is to be done, other than what I've suggested so far already? I think informal chat sessions are a great idea, just to get people in the room (here's the link, as it's kind of hard to find) and talking. Give it six or eight hours instead of two, as we're spread across the globe, and those in India/Southeast Asia likely won't be up and about at the same times as those of us in the US or Canada are. If you come in late, you can scroll up to see what you've missed, and at the very top of the page is a load older messages button to go back even farther in history. I don't think they necessarily need to have a specified topic or topics to begin with, but perhaps some suggested topics could come in handy if the smalltalk falls short. Just try to get to know your fellow biologists a little better: where they come from, what they do, what they're interested in, etc. Just normal friend-making stuff.
After a couple of these, or perhaps interspersed with them, we could do topic discussions, although they'd have to be chosen very carefully, as (for example) I have very little interest in theoretical population biology and all of those equations that Remi.b loves to pour out (no offense), but someone else couldn't care less about the tumor microenvironment and immunotherapy, my current field of work.
In conclusion (finally!), I'd like to repeat what I said at the top: chat is what you make of it. If you want more interesting discussion, get in there and put something out for discussion. Make small talk. Get to know people better. Joke (kindly). Don't worry about appearing to be a brainy nerd, but don't show off your massive knowledge just to show off. Relax, and have fun.
insert topic hereoninsert date/day hereatinsert time here, come and join me". Why make something so formal as a chat session? If you want to discuss a topic then do it, I've seen many impromptu discussions come up in chat, the worst that will happen is that there is no one around that wants to discuss it (but that problem will affect formal chat sessions too). $\endgroup$