Not a lot. At FOSDEM (at least for the last 10y, I have been attending), you have four kinds of talks:

* Lighting talks/short talks: Most of the time, you may not have Q/A if the speaker talks too long but you can catch they off stage to talk about it. So you keep the live aspect.

* Big/Popular talks/Main roam (Janson): You don't ask Q/A during those presentations so it would not change a lot.

* Mid-sized talks/roams: It depends on the speaker how much interaction, he wants.

* Tiny roams: There you will loose the jokes and the fun going on with well-know speakers in their communities.

I think we will see less informal/fun talks because the streaming format does not easily allow the spur of the moment joke/question. The quality of the speaker will really during those Q/A moments but on a time management side, the good news is that you have less time-keeping to do with a prerecorded streaming event if each talks has his channel.

IMHO that's generally a good model: it reduces issues with the setup or speakers internet connections, and allows the speaker to stress-free answer questions in chat during the talk.

It can make sense to have a real-time portion so that attendees get more of a sense of attending a live "event." But I agree that my experience as someone helping to run some events is that it makes sense to pre-record most sessions. There's a lot less sense of working without a safety net, fewer problems, and more time to focus on making those parts that are live go as smoothly as possible.

Of course and it will not be the same;

For the ccc conference rc3, linus said something in direction of 'lets not do that again'.

At least for me, i go to Fosdem for all the talks of course but also to see people, dring belgien beer, eat, freeze, have wet shoes and enjoy the sun on the second day for 1-2 hours.