you are having a bit of NOSTALGIA GAS, which is fine, I think everyone has a bit of this from time to time. There must have been a time you told yourself..... you're never going back to a 6D!
Kind of like the nokia days, I'm never going back to a larger phone
I think you should sell the body and lenses if not in use. They are big, bulky, and tie down some funds. In the end, you may repurchase them, selling them now just frees up funds in case GAS takes you elsewhere.
I do keep my set of fast zooms along with fast primes, simply because I suffer from similar GAS at times, and I simply shuffle my gear around and I'm done. Sometimes I like shooting fast primes, sometimes fast zooms, most of the time, lightweight primes. Not the most practical thing, but I do use all quite a bit, and my lightweight kit gets used the most by far. I remember shooting JUST the 6D and 50L like it was yesterday, a hugely enjoyable combo, that produced many keepers. So simple and so productive, that said, the ship has sailed, and that's as far as my nostalgia goes
You could be on to something. But I have been wanting back the 6D for a while.
Go back to B&H and see what they'll give you for your gear. They buy and sell used equipment. Also, see if they have a used 70-200 f/4 IS, or see if they will give you a good deal on a new one (not very likely, but no harm asking). Adorama also buys and sells used gear. Will you get The Best Price™ from B&H or Adorama? I think you'll get a fair price, which itself is a good thing.
Dump the 5D4, the Tamrons, get the 70-200, and then do these two things.
1. Enjoy your 6D and glass!
2. Don't look back.
I'm pretty sure I will not to get what I want as trades at either B&H or Adorama. Still not sure how much to ask though. The 5D4 is almost two years old now and new is going for $3,099.00 at both stores. The lenses have held their value (IMO). So maybe that won't be so hard a hit. I recently upgraded my laptop to a touch bar, but I also been wanting to upgrade my 2011 iMac for a 5K iMac. So selling these items will certainly help in that dept.
But yeah, I am close to putting the 5D4 + Tamrons up for sale. Just have to figure out how much.