Correct. Well, to be precise, you also need the seed S (besides the master public key and a single, non-master private key). Electrum uses the master public key itself as the seed, while Armory uses what it calls a chaincode. However, this doesn't make a difference because for practical purposes, i.e. in order to be able to generate the chain of public keys, both the master public key and the seed will be stored together on the same machine.
what you write is correct, but for Electrum users, the word "seed" refers to a secret number used to derive their master private key.
what you call "seed" here is Electrum's master public key.
I am just writing this in case users who are familiar with Electrum find it confusing. :-)
Yes, by "seed" I was referring its meaning in gmaxwell's original post, which is different what Electrum calls its seed.
Here is a specific suggestion for Electrum: I want to take k pieces of paper, divide the wallet seed into n parts and write on each piece of paper m of the n parts. The pieces of paper will be stored in different locations, so that someone needs access to several locations simultaneously in order to recover the wallet seed. Now, the seed being 128bit long, simply dividing into n shorter parts doesn't work even for n=2 because 64bit is not secure enough against brute force attacks. Each part should be 128bit as well. Maybe Electrum can print out n seeds, 128bit each, which XORed together give the wallet's seed?