Estate planning: how can I ensure my bitcoins are inheritable? What are good ways to ensure my bitcoins can be inherited by my family
when I die or become permanently incapacitated?

I think there are probably two significantly different situations to
account for, each with different requirements:

Hot wallet inheritability

I want my family to be able to inherit the bitcoins from my hot wallet,
but I'm not worried about them stealing those bitcoins or monitoring my
public transaction history while I'm still living.

Cold wallet inheritability

I also want my family to be able to inherit the bitcoins from my cold
wallet, but I'd prefer a solution that prevents them from being able to
spend the bitcoins while I'm still alive. If possible, I'd also like to
prevent them from determining my balance while I'm still alive.


It is acceptable for the solution to require periodic activity from
me, such as moving my bitcoins every six months. For example, your
answer may assume that
OP_CHECKLOCKTIMEVERIFY
has become consensus-enforced, as that's likely to happen within the
next few months---and I hope to live that long.
Because I tend to use strong encryption when available, assume that
all my data will be lost at my death unless I've specifically backed
it up for other people to use.


I use Bitcoin Core for both my hot and cold wallets (with separate wallet files), but solutions for other Bitcoin software are welcome.
Points for Hot Wallet Inheritability:  


Lower exposure to risks - use hot wallets that are BIP 39 compliant and share your 12 to 24 recovery passphrase and associated password in advance.
Higher exposure to risk - share passwords on your devices that have hot wallets.  BIP 32 compliant wallets make it easy to have the same logical wallet deployed on to multiple devices (e.g., cell phone and tablet). 
Highest exposure to risks - preload multiple instances of hot wallets on their devices.


Points for Cold Wallet Inheritability:


BIP 38 compliant paper wallets allow your paper wallet's Wallet Import Format (WIF) private key (Base58Check encoded) to be AES encrypted, recoverable with a password.  If you are worried about hiding the amount of the funds, just be sure your paper wallets do not have associated cryptocurrency addresses printed on them. (Cryptocurrency addresses are derived from associated associated private keys. If the private keys are encrypted, and an associated public addresses are not exposed, the amount of funds saved can remains a secret.)  
A multi-party escrow service is required to ensure your funds don't get spent before the "big event". Either an on-blockchain multisig service can be applied with m of n signatures being required or an off-blockchain Shamir's Shared Secret can be applied.  The take-away point is that a sealed will is used as a mechanism (or a trusted 3rd party) is used to release the funds. 
High tech approach, less privacy where m of n signatures come together for an on-blockchain approach, which doesn't have the desired privacy.
Low tech approach, desired privacy where enough Shamir Shared Secrets need to come together to reconstitute a passwords used by BIP 38 compliant paper wallets. Each heir could have their own unique paper wallets with a common passwords shared across all the wallets. It is also easier to change a will using this approach. The redistribution of updated shared secrets also gets the point across that either you are upset or happy with the behavior of your heirs.


FYSA, Some hot wallet application directly support the importation of BIP 38 encoded keys. 

WARNING: As with all backup and recovery processes, perform dry-run tests in advance to be certain the backup and recovery processes are working properly.  Also, perform key generation on a computer (preferably a spare one) that will never be connected to a network again,
print on a network enabled printer private cryptocurrency keys unless they are encrypted using something like BIP 38.