Well, their new show starts on Amazon this fall. So assuming fall of 2016, 2017 and 2018 to fulfill their Amazon contract, that means they wouldn't be available for the BBC until 2019 earliest and that's if there's no non-compete clause which keeps them off the air for x years afterward. That's a long time in TV years. By then the BBC better have found a working formula to save Top Gear or it'll be dead.
Given the size of the their deal with Amazon they're not in any hurry to go back to the BBC. They're getting far bigger salaries and a much larger per episode budget. That allows them a lot of freedom, for the original team Amazon is a much better place to be.
And yeah, too many presenters. I'm wondering if that was the original plan or were their roles bumped up when early on it became apparent that Chris and Matt were not going to be very good? They do need to cut back though, three is plenty and more than that people start to get lost. That Eddie Jordan guy might as well not have been there at all.
Usually once a team moves over onto another "TV channel", they stay there and/or disappear (fade away).
E.g. Fifth gear (original top gear team, from a while ago).
Returning to the original channel, is rare. (I'm using the term "TV channels", loosely because there are so many media outlet options these days).
When I first noticed "Eddie Jordan", in the him taking the railways episode. I thought/assumed that he was just a guest. I did not realize he was suppose to be a presenter, he just did not seem right for such a role.
On the other hand I find "Eddie Jordan", seems to have some of the annoying "James May" type of concept (don't get me wrong. I REALLY like James May. But there is some tension, which adds to the "fun" elements of the Jezza team). So he does have at least some purpose.