Thru axle (TA) has been around for about 7-8 years on mid-priced and up MTBs, mostly on front only. It is relatively new for MTB frames to incorporate TA. TA is a boon to some, but for many it is another solution-looking-for-a-problem. I never lost a wheel MTBing with std QR axles.
AFAIK, Trek 920 is the only touring bike to incorporate TA. It seems even less likely that TA is an innovation actually needed in normal touring. If you are touring so that TA does make sense, then you probably need to use a suspended BoB trailer or similar since no std rack could take that kind of beating for long - in which case you could tour on any kind of bike, like a 29/27.5 MTB.
Actually if you are riding in such conditions, you will quickly realize you need to find a better route to make any progress - in which case you will then want a more std touring bike. If you make good route & timing decisions, then most unusual bicycle technologies become unnecessary and rendered simply a sales gimmick. Disc brakes are overkill for some scenarios/regions/users. Discs excel in rain, but in dry weather they transform to little more than 2-3 extra pounds of complicating componentry. I have found disc brake in front only to be a good compromise in brake performance/added weight, since the front does majority of actual stopping.