NO. If they do this, they better have a banking system, because I like having backup armour and weapons. If you are going to do this, have a large grid and outline items with blocks, and if you can turn or move them to fit into the bag, then you can carry it. period. That would be good... because you are forgeting that this world has magic. weight can be lowered in bags, and the animals trainers use would allow a larger grid, not a larger weight carring system.
also, If your pet dies, can you revive him? or do you lose all your items?
If you die, does your pet teleport to your position?