I made this exact upgrade. I'd been using an xsi that was a hand-me-down and it's a surprisingly capable camera. Anyway, I wanted more iso and video so bought a 6D with the 40mm STM.
It's a phenomenal camera. I'll be happy using it until the day it literally falls apart. The xsi is still used - I always liked its low iso performance and the colours are great etc. it's a tough little bugger that just won't die. So keep yours as a backup.
Just make the most of what you have, the 16-35 would be good because we have very narrow streets in London and especially Paris. Personally speaking, I just slap the 40mm STM on the 6D for walking around/travel. Its so convenient and the optics are as good as it gets regardless of price. Maybe take one as a body cap
With this ongoing wait we seem to be in, I'm starting to get the impression that Canon will release the 7D2 and 70D simultaneously, or near enough, with the same new sensor. 700D will get it at some point in summer.
If they were going to release it as a warmed-over 60D, they would have done it already to coincide with the 650D.
I guess we'll just have to wait and see. If its a big enough let-down, the 6D should be a fair bit cheaper by then anyway.
PJ1974 - I think you're right, people often read between the lines and see something completely subjective.
To paraphrase Maeda, he says there may room for more FF bodies in the lineup - I'm struggling to see where they will fit in... Eg: which side of the 5D would they go, better or worse?
Maybe they will drop the pentaprisms and have a model on each side: a 1DX feature set but with EVF to fit between the standard 1D and 5D and then an EVF model based on the 6D that would fit in just below the latter. Basically two EOS M Pro models.
I honestly think we'll see new sensors this time around. I also wouldn't be surprised to see the 7DII to be shown off at Cp+, maybe given a rough release date, like spring... It just won't be released immediately.
Canon know full well how old that 18MP sensor is and they haven't been sitting idle for the last three years. It would be immensely stupid to warm-over the 60D like people are saying will happen...