The issues I have with through axles are mainly to do with maintenance. With QR you have the ability to use the NBT-2 tool to remove the rear cassette in order to replace a drive side spoke or to just access the freehub for maintentance. I am not aware of a similiar tool for through axles and such tool could be difficult to create simply because of the host of different thru axle standards available. Now it's not THAT big of a deal to carry a chain whip, cassette socket and a lever for it but i took off little under 2 pounds from my touring tool set when I replaced those tools with the NBT-2 which weighs 20 grams or so.

There's also the availability issue. Quick releases can be found practically everywhere and in a pinch a threaded rod would probably work. I'd wager one could limp to the next maintenance possibility with a smart use of brake cables in a pinch. (not the safest option obviously, especially in the front). On top of that quick releases are very compatible since there's only a few sizes. A too long a skewer won't hurt and a too short one can be made to work in the right conditions.
With a thru axle while breaking one is not really probable, if it does happen, finding a replacement can be extremely tricky even in a big city with well stocked bike shops. They may have one standard on the shelf but do they have your standard? So worst case one needs to carry extra or mail order.

Also I'm not sure if the benefits are there for touring. I've developed a method where I can get my wheels and discs centered perfectly every time I put them on. I have a hex skewer and with 7Nm of torque the disc is centered within the caliper. I can get to pretty darn close to the 7Nm without a torque wrench on the road by just torquing the skewer until the disc is centered in the caliper. Of course the bike needs to be in a position which allows for straight alignment.
I also doubt touring has that many situations where one would really need the added front end stiffness. Depends on the type of touring of course but I've gone pretty fast on road with my fully loaded tourer, leaning into hairpins with as much grip as I was comfortable with and front end stiffness was not the thing on my mind at the time.

Thru axles work for mountain bikes where the front and rear suspension can make the forks a bit flexy. A thru axle stiffens this combo significantly.
On road it helps with disc brake use especially if one wants to use different wheelsets, needs to change a flat on the road (much more common than on tour since thin tires and all that) and I suppose on sprints or other hard efforts the increased stiffness helps with better tracking of the bike.
But I don't see those things in touring.