I think it will probably happen next year.

But it's more nuanced than that. In order to prevent everyone withdrawing at once, only a set number of validators will get to unstake per epoch. The logic behind how this works is still TBD, but last I checked early stakers will get priority (i.e. Ethereum Foundation). So even if the Shanghai fork happens this spring, it could be much longer before you get a chance to withdraw if you were a later staker.