I agree that D&Dnext is highly likely to have PCs built in terms of capabilities that are both fictional attributes/belongings of the PC and player resources to deploy in the course of playing the game.
These are likely, at a minimum, to include weapons, spells and a range of inherent talents.
But is it a given that they must include 10' poles, iron spikes and torches? And even if they do include these as a default, you yourself note that there are options other than encumbrance for ratioining these things. (The most obvious one is rationing by cost - and spending money to buy things is a one-off burden on playtime and can be done as part of game prep, whereas encumbrance tends to be an ongoing burden on playtime that has to be continually tracked as things are picked up and used/put down.)
Although dungeon play has been one perennial focus of D&D, it was not the only focus and arguably, from the time of Oriental Adventures and Dragonlance through to the end of 2nd edition (a period of around 15 years), was not the primary focus (at least of published materials - extrapolating from these to actual play is of course a tricky business).
I think that encumbrance is likely to be in the core, because it has been in every edition of D&D, but I don't think it is essential that it be there. As one of the most widely ignored of rules subsystems, it is ripe for change.