I think that the question is first, which camera. Then, which lens. I liked my Canon EF-S 60mm f/2.8 on my 60D - good focal length for not having extraneous stuff between you and flower - most flowers were at 1:2 to 1:3, though. Tilt screen is a GREAT macro accessory, as is a tripod without center column (flatten legs out to 180 degrees to sit tripod flat on ground) for flower and mushroom photography, unless you carry both tripod and beanbag. I have seen the Sony full frame new 90mm macro lens get some rave reviews from A7R/R2 users. But if your 90mm macro-Elmar is still working, just get another Sony APS-C if you do mostly tripod work. You don't need autofocus for plants / flowers, only for moving creatures (depending - I sometimes just set manual focus at the desired magnification and follow the bee or other slow mover from plant to plant). An IBIS would be wonderful for hand-held semi-macro, but if you aren't hand holding, you don't need IBIS, just a remote shutter release and a tripod. Maybe the A6000 is for you - there's a lot of bells and whistles in the newly announced A6300 that you might not need.
I am curious - how do you handle the battery life problem of non-SLRs on week-long hikes? Just start off with a bunch of charged batteries? Charger plus one of those super-batteries people use for recharging phones? Solar? I should add, I tend to judge all mirrorless cameras by my experience with the Sigma DPM3, a great sensor and lens attached to a lousy LCD and worse battery. BTW, I have used a 52mm 2-element achromat +5 diopter lens on the front of the DP3M with decent results.