If you're dead set on any particular unis in the future, then there's a chance that they might be one of the few unis that outright dismiss BTEC students. However, for the vast majority of unis, you'll be fine with a BTEC Extended Diploma.
And yes, for Media especially, you might find that doing the one Extended Diploma in Media is more suited to you than doing 3 distinct A-levels, 2 of which you might not care about.
The main worry if you're a really ambitious student is that you won't be able to go to Cambridge with a BTEC(at least according to the policy on their website)