If we're talking clean slate here, I'll just recommend the one camera/lens combo I would consider worth going for from my very own point of view: The Olympus E-M1 II with 12-100mm f/4 PRO. Why? You get a catch-all combo with fantastic overall feature set and very good image quality that's not too big (though bigger than your current
setup).
I've tried the lens - it's great in terms of usability, and in absolute terms (say, compared to the Sony/Zeiss 55mm), it's pretty compact, while all reviews so far found it to be plenty sharp and supremely versatile.
As for the camera: I haven't used it, but I've handled every other OM-D (including the E-M1), and all of them where convincing cameras - and when taking into account the impressive number of improvements in the E-M1 II, if it's a one-off solution you're after, it's kind of no-brainer.
If you really let go of everything, the funds shouldn't be that big of a problem. An it's the only new camera that really got me thinking - not even the Nikon D500 had that much pull. Nothing against Canon, btw. - I just think you'd need to go for one of the pro bodies to get anywhere near the performance of the E-M1 II, and that'd land you with one beefy setup indeed ...
Second suggestion, somewhat against the whole mirrorless wave: Nikon D750 (the best bang-for-the-bug FF DSLR at the moment, IMO - and not that big and heavy in absolute terms) with your choice of either Sigma or Tamron (or Nikon, come to that) primes - I chose Sigma, but I think you'd probably lean towards Tamron because of size and weight considerations - or one of the many capable zooms available: Nikon 24-70mm f/2.8E (or G), Nikon 24-120mm f/4G, Sigma 24-105 f/4 Art (my choice - but I own the Olympus 12-40mm as well), Sigma 24-35mm f/2 Art (see below ...), Tamron SP 15-30mm f/2.8 etc. - all solid to great performers, and extremely useful; pick your poison! It may not sport 36Mpix, but the files are a joy to work with, and with the right lenses, there are no real limits to what you can do. If I'm unsure what camera to pick, I grab the D750 and add a suitable lens or set of lenses. Lastly, the honorary mention: The Nikon 35mm f/1.8G ED and 85mm f/1.8G are great lenses, really quite small and light, and cheap ... if you add the somewhat lesser Nikon 50mm f/1.8G, you can put the camera and three lenses in quite a small bag, no problem. And the 20mm/24mm/28mm f/1.8 primes are all very good, too ...
Finally, on a more personal, but maybe also quite revealing note: The E-M1 II is the only camera I would consider giving up my Nikon APS-C stuff for - it's so powerful it would make me forget the (slight) loss in maximum IQ. But I'm still attached to my D5500 with Sigma 18-35mm f/1.8 Art - this combo is such a revelation ... But seeing where you're coming from, I'd never dare recommend this - it would feel too much of a downgrade, I guess. But the Sigma zoom is worth every ounce and cent ...
M.