1, I highly doubt Theo and the organization believe they're any less likely to win the 2017 WS because they won the 2016 WS. I mean it's so illogical to how they act I'd be shocked if the idea was even entertained.
2. I think Theo would make the right "move" in an Arrieta trade (I.e they get back a long term potential TOR) but I doubt they'll do it to just do it and improve the team beyond 2017. The Cubs could say to themselves "Let's sign Ross to an incentive deal, hope he's available in 2018 and beyond and then go after Otani and let Jake walk". They could just slot Otani in to the Montero/Arrieta money, a guy like Tyson Ross in to the Lackey money, and then save a ton on Montgomery and bullpen arms compared to Hammel/etc.
3. The Cubs, for the first time maybe ever, have projectable arms in a timeline that's actually present. After the years that Cease and Clifton had (with de La Cruz just a tad below that), the Cubs have late 2018/2019 arms there. Add in Lester, Montgomery, and Hendricks still being team control and the hope to get Otani, the desire and need for TOR SP in the future isn't as huge as it may have been just 12 months ago.
4. I wouldn't be surprised if the Cubs are done. Maybe the Ross thing changes their mind (a guy they've liked + have history with + projects perfectly for their system + no compensation + down price) but I could see a world where Theo and the FO just lets this breathe a little bit. Looking at the top end guys, you have Happ get a full year between AA/AAA and then he's maybe a mid 2018 call-up. Eloy ends in AA this year and ends in AAA next year and he's potentially a 2019 (if Heyward leaves). Candelario could be a playable CIF backup.