As a Rek'Sai Main since her Release Day, my PBE thoughts
About me: I am a high silver player, ended gold last season. I picked up Rek'sai the day she was released and has been my main ever since. Oh the sad times of 13 patches of nerfs back to back to back. From a fierce land shark to a knock up bot. Even though I still played her damage top on occasion, it was still sad to see the power in her disappear. Then a light at the end of the tunnel appeared and a mini-rework to get her to her roots was announced and man was I excited.
So I finally got to play the new
yesterday on the PBE after a "few brief hours" of waiting cough cough sat on PBE waiting like 13 hours cough cough. Oh the excitement was too much to bear. And the ult? So Satisfying (though deep down I will always miss old ult QQ new one is better tho). I played her top bc its the most fun, and the build i think changes a bit from 7.10 to 7.11.
First thing I noticed was early game (like pre-items) feels way weaker, but after the
it was great).
my build top (its wonky and changes a bit depending on situation but heres the gist:
first:
I know, i know. Tforce lol. sheen gives SO much damage and attack speed, is great. if it snowballs early you can 1v4 mid game. Easy. (It worked bc im good :P)
Now I tried this build on rework and I think you HAVE to build some tank now. With her new ult, diving into team for the execute is risky and you will probs get 1 or 2 kills but more survive-ability is needed so I would change it to this i think:

Choose 2 on your lead vs their team comp:

I need to play it more to find out how exactly Top Rek'Sai can be itemized (especially early). And especially changing it up depending on enemy team comp and how ahead I get. Needless to say I am stoked to play this on normal server with my nice 30ms (on PBE its around 80 so it feels weird)
For my jungle peeps out there yes I play her jungle mainly, but top rek is way more fun lol
in jungle id say replace one of the optional items with warrior. so
if you can first buy
do it, if not go with
into
. Without jungle clear from tiamat u will need sustain.

and then either
or
or 
I will be streaming tonight some gameplay of the new Rek'Sai. You can find me at: https://www.twitch.tv/phsyrik