Honestly, it's a hard thing to balance. There's nothing more annoying than inventory Management especially when there is so much useless junk that I'm managing. Multi-select would certainly make it faster and less cumbersome.
I think an Auto-sell or auto-send to camp is fine with limitations. Maybe it is restricted to certain areas so encumbrance and even picking up useless junk has some meaning and purpose.
For example, if in the goblin camp, it is disabled. If you are in Grymforge, it is disabled until the conflict there is resolved.
But then, if you do that, shouldn't you then also restrict fast travel and long rest? Ah! And here we go again. The debate continues. Should we limit fast travel, long rest and send to camp, or just let players play however they want? Why? Because all these things go together. If you restrict one, all the others must also be restricted otherwise what's the point?
I can run through most content in the EA in about 6-8 hours with a strong group of 3 other people that know what they are doing. The biggest time-sink isn't the combat (which is very fun) but inventory management and selling stuff - which is just work.
With a new group I have to train people on how to handle the entire process of marking as wares and sending to people to sell (and a LOT of other stuff). This game has a HUGE learning curve as it is, and I say this as someone who has demonstrably trained legions of players.
I would emphatically discourage doing anything like what you just described to make things more complicated or difficult when it comes to inventory management. We need to do the opposite to make inventory management more painless and less time-consuming - even if it doesn't follow strict rules of having people be near each other.
