They'll change the format, I don't think you'll see everyone every week. What I like about this is that it seems to be more a return to older top gear, actually focused on the cars instead of just dicking around (which I did enjoy, but it got repetitive). They know if they try to copy the format they had with hammond/may/clarkson and go head to head for the same viewers they wouldn't stand a chance. So probably less studio time/news/star in a reasonably price car (all of which were my least favorite bits of the show)
In regards to Matt Leblanc, I think it's pretty big unknown if it will work but if anyone watches his newer show Episodes, I think that's much closer to his real life personality than the idiot he played on friends, I can see a lot of banter between him and chris harris.
Overall it was always going to be impossible to replace the trio, this looks like a good way to start fresh.