As the sprint days of PyCon US where I will be and participate. I can attend to the Core Dev Sprint in London. Brussels -> London is not really. About the date, @larry is right, there is the PyCon UK in mid-september (Cardiff). 15th September is also my birthday but the last year I was at PyCon UK 
One more collision to note: PyCon-PL will be held from September 12-15.
In 2017, for my “Python Tour 2017” t-shirt, I had counted ~ 50 or 60 major Python events around the world. The risk of a collision with an other event is high.
Will there be a core dev counterpart for me to work with for organizing the September sprint? I am not sure what has been done in the past, but looking at @eric.snow’s post an invitation has gone out to all core devs. I don’t mind doing that part either, I just don’t want to step on any toes.
I’m in London working with Mario Corchero in the organisation of the sprint from the Bloomberg side. Not sure if I understand you message correctly, but we have not sent anything still (invitations or otherwise).
Thank you, Pablo. I see your email and will follow up tomorrow!