Krack WPA2 decrypt only some small pieces of packets I have gone through the paper (PDF) available at krackattacks.com.

However, from what I understood you force a key reinstallation causing you a nonce reuse over 2 blob of data. As it is a keystream, you might be able to decrypt the data.

Limitations are:


You MUST know clear text of one of both data
It is one shot as the counter gets incremented, you need to perform another key reinstallation to be able to decrypt further data


This doesn't sound very practical in my point of view, am I missing something?
It's depressingly practical. And you can reset the key multiple times, getting the same key stream every time. So if the third or forth time you get guessable plain text content in different parts of the key stream you can combine this until you have everything. 
Your computer does all kinds of communications, it polls stuff, it makes DNS lookups it uses standard headers and standard protocols all of this produce lots of guessable data. On a not busy network we can also use packet sizes to help us find our guessable data. 
In reality finding known plain-text is not difficult.